Fix crash in goto-def on @override

When the base type is not defined, getDefinitionFromOverriddenMember
will have its type as errorType, which has no symbol. The error handling
previously only handled the case of no baseType at all -- which I'm not
sure ever actually happens.

Author: sandersn

src/services/goToDefinition.ts

@@ -176,7 +176,7 @@ namespace ts.GoToDefinition {
 
         const name = unescapeLeadingUnderscores(getTextOfPropertyName(classElement.name));
         const symbol = hasStaticModifier(classElement)
-            ? typeChecker.getPropertyOfType(typeChecker.getTypeOfSymbolAtLocation(baseType.symbol, baseDeclaration), name)
+            ? baseType.symbol && typeChecker.getPropertyOfType(typeChecker.getTypeOfSymbolAtLocation(baseType.symbol, baseDeclaration), name)
             : typeChecker.getPropertyOfType(baseType, name);
         if (!symbol) return;
 

tests/cases/fourslash/goToDefinitionOverrideJsdoc.ts

@@ -0,0 +1,16 @@
+/// <reference path="fourslash.ts" />
+// @Filename: goToDefinitionOverrideJsdoc.ts
+// @allowJs: true
+// @checkJs: true
+
+//// export class C extends CompletelyUndefined {
+////     /**
+////      * @override/*1*/
+////      * @returns {{}}
+////      */
+////     static foo() {
+////         return {}
+////     }
+//// }
+
+verify.goToDefinition(['1'], [])