Do not load the source file just to get an irrelevant SourceLoc (ROOT-7111).

Author: Axel-Naumann

clang/lib/Lex/Lexer.cpp

@@ -813,6 +813,10 @@ SourceLocation Lexer::getLocForEndOfToken(SourceLocation Loc, unsigned Offset,
       return {}; // Points inside the macro expansion.
   }
 
+  // Don't hit the file system for ASTReader tokens.
+  if (SM.isLoadedSourceLocation(Loc))
+    return Loc;
+
   unsigned Len = Lexer::MeasureTokenLength(Loc, SM, LangOpts);
   if (Len > Offset)
     Len = Len - Offset;