katex [nfc]: Replace classFound local with a default case

Before this change, all cases of this switch statement either
continue the loop, or throw, or set classFound to true.
The error therefore gets logged just if none of the cases matched.

So we can express the same behavior with a default case.

Author: gnprice

lib/model/katex.dart

@@ -150,33 +150,28 @@ class _KatexParser {
     var index = 0;
     while (index < spanClasses.length) {
       final spanClass = spanClasses[index++];
-      var classFound = false;
-
       switch (spanClass) {
         case 'base':
           // .base { ... }
           // Do nothing, it has properties that don't need special handling.
-          classFound = true;
+          break;
 
         case 'strut':
           // .strut { ... }
           // Do nothing, it has properties that don't need special handling.
-          classFound = true;
+          break;
 
         case 'textbf':
           // .textbf { font-weight: bold; }
           styles.fontWeight = KatexSpanFontWeight.bold;
-          classFound = true;
 
         case 'textit':
           // .textit { font-style: italic; }
           styles.fontStyle = KatexSpanFontStyle.italic;
-          classFound = true;
 
         case 'textrm':
           // .textrm { font-family: KaTeX_Main; }
           styles.fontFamily = 'KaTeX_Main';
-          classFound = true;
 
         // case 'textsf':
         //   // .textsf { font-family: KaTeX_SansSerif; }
@@ -186,96 +181,81 @@ class _KatexParser {
         case 'texttt':
           // .texttt { font-family: KaTeX_Typewriter; }
           styles.fontFamily = 'KaTeX_Typewriter';
-          classFound = true;
 
         case 'mathnormal':
           // .mathnormal { font-family: KaTeX_Math; font-style: italic; }
           styles.fontFamily = 'KaTeX_Math';
           styles.fontStyle = KatexSpanFontStyle.italic;
-          classFound = true;
 
         case 'mathit':
           // .mathit { font-family: KaTeX_Main; font-style: italic; }
           styles.fontFamily = 'KaTeX_Main';
           styles.fontStyle = KatexSpanFontStyle.italic;
-          classFound = true;
 
         case 'mathrm':
           // .mathrm { font-style: normal; }
           styles.fontStyle = KatexSpanFontStyle.normal;
-          classFound = true;
 
         case 'mathbf':
           // .mathbf { font-family: KaTeX_Main; font-weight: bold; }
           styles.fontFamily = 'KaTeX_Main';
           styles.fontWeight = KatexSpanFontWeight.bold;
-          classFound = true;
 
         case 'boldsymbol':
           // .boldsymbol { font-family: KaTeX_Math; font-weight: bold; font-style: italic; }
           styles.fontFamily = 'KaTeX_Math';
           styles.fontWeight = KatexSpanFontWeight.bold;
           styles.fontStyle = KatexSpanFontStyle.italic;
-          classFound = true;
 
         case 'amsrm':
           // .amsrm { font-family: KaTeX_AMS; }
           styles.fontFamily = 'KaTeX_AMS';
-          classFound = true;
 
         case 'mathbb':
         case 'textbb':
           // .mathbb,
           // .textbb { font-family: KaTeX_AMS; }
           styles.fontFamily = 'KaTeX_AMS';
-          classFound = true;
 
         case 'mathcal':
           // .mathcal { font-family: KaTeX_Caligraphic; }
           styles.fontFamily = 'KaTeX_Caligraphic';
-          classFound = true;
 
         case 'mathfrak':
         case 'textfrak':
           // .mathfrak,
           // .textfrak { font-family: KaTeX_Fraktur; }
           styles.fontFamily = 'KaTeX_Fraktur';
-          classFound = true;
 
         case 'mathboldfrak':
         case 'textboldfrak':
           // .mathboldfrak,
           // .textboldfrak { font-family: KaTeX_Fraktur; font-weight: bold; }
           styles.fontFamily = 'KaTeX_Fraktur';
           styles.fontWeight = KatexSpanFontWeight.bold;
-          classFound = true;
 
         case 'mathtt':
           // .mathtt { font-family: KaTeX_Typewriter; }
           styles.fontFamily = 'KaTeX_Typewriter';
-          classFound = true;
 
         case 'mathscr':
         case 'textscr':
           // .mathscr,
           // .textscr { font-family: KaTeX_Script; }
           styles.fontFamily = 'KaTeX_Script';
-          classFound = true;
 
         case 'mathsf':
         case 'textsf':
           // .mathsf,
           // .textsf { font-family: KaTeX_SansSerif; }
           styles.fontFamily = 'KaTeX_SansSerif';
-          classFound = true;
 
         case 'mathboldsf':
         case 'textboldsf':
           // .mathboldsf,
           // .textboldsf { font-family: KaTeX_SansSerif; font-weight: bold; }
           styles.fontFamily = 'KaTeX_SansSerif';
           styles.fontWeight = KatexSpanFontWeight.bold;
-          classFound = true;
 
         case 'mathsfit':
         case 'mathitsf':
@@ -285,13 +265,11 @@ class _KatexParser {
           // .textitsf { font-family: KaTeX_SansSerif; font-style: italic; }
           styles.fontFamily = 'KaTeX_SansSerif';
           styles.fontStyle = KatexSpanFontStyle.italic;
-          classFound = true;
 
         case 'mainrm':
           // .mainrm { font-family: KaTeX_Main; font-style: normal; }
           styles.fontFamily = 'KaTeX_Main';
           styles.fontStyle = KatexSpanFontStyle.normal;
-          classFound = true;
 
         // TODO handle skipped class declarations between .mainrm and
         //   .sizing .
@@ -377,10 +355,11 @@ class _KatexParser {
         case 'mopen':
           // Ignore these classes because they don't have a CSS definition
           // in katex.scss, but we encounter them in the generated HTML.
-          classFound = true;
-      }
+          break;
 
-      if (!classFound) _logError('KaTeX: Unsupported CSS class: $spanClass');
+        default:
+          _logError('KaTeX: Unsupported CSS class: $spanClass');
+      }
     }
 
     String? text;