[clang-tools-extra] [clang-tidy] Fix crash on invalid file extension options (PR #227869)

[Zeyi Xu via cfe-commits]

================
@@ -245,15 +245,24 @@ void ClangTidyContext::setCurrentFile(StringRef File) {
   WarningAsErrorFilter = std::make_unique<CachedGlobList>(
       StringRef(getOptions().WarningsAsErrors.value_or("")));
   static const std::vector<std::string> EmptyFileExtensions;
-  if (!parseFileExtensions(getOptions().HeaderFileExtensions
-                               ? *getOptions().HeaderFileExtensions
-                               : EmptyFileExtensions,
-                           HeaderFileExtensions))
+  const bool ValidHeaderFileExtensions = parseFileExtensions(
----------------
zeyi2 wrote:

I think this can be simplified to the following:

```diff
   WarningAsErrorFilter = std::make_unique<CachedGlobList>(
       StringRef(getOptions().WarningsAsErrors.value_or("")));
   static const std::vector<std::string> EmptyFileExtensions;
   if (!parseFileExtensions(getOptions().HeaderFileExtensions
                                ? *getOptions().HeaderFileExtensions
                                : EmptyFileExtensions,
-                           HeaderFileExtensions))
+                           HeaderFileExtensions) &&
+      DiagEngine)
     this->configurationDiag("Invalid header file extensions");
   if (!parseFileExtensions(getOptions().ImplementationFileExtensions
                                ? *getOptions().ImplementationFileExtensions
                                : EmptyFileExtensions,
-                           ImplementationFileExtensions))
+                           ImplementationFileExtensions) &&
+      DiagEngine)
     this->configurationDiag("Invalid implementation file extensions");
 }
```

This keeps the change smaller while preserving the intended behavior. 

WDYT?

https://github.com/llvm/llvm-project/pull/227869