Fix a crash that can occur when a #pragma handler eats to the end of the

line, and when the pragma is at the end of a file.  In this case, the last
token consumed could pop the lexer, invalidating CurPPLexer.  Thanks to
Peter Thoman for pointing it out.

llvm-svn: 73689

clang/lib/Lex/Pragma.cpp

@@ -93,7 +93,7 @@ void Preprocessor::HandlePragmaDirective() {
   PragmaHandlers->HandlePragma(*this, Tok);
   
   // If the pragma handler didn't read the rest of the line, consume it now.
-  if (CurPPLexer->ParsingPreprocessorDirective)
+  if (CurPPLexer && CurPPLexer->ParsingPreprocessorDirective)
     DiscardUntilEndOfDirective();
 }