[clang] Fix Unintialised char *CommentLexer resulting in potential UB. (PR #210067)

[Aaron Ballman via cfe-commits]

================
@@ -240,7 +240,7 @@ class Lexer {
 
   /// One past end pointer for the current comment.  For BCPL comments points
   /// to newline or BufferEnd, for C comments points to star in '*/'.
-  const char *CommentEnd;
+  const char *CommentEnd{nullptr};
----------------
AaronBallman wrote:

```suggestion
  const char *CommentEnd = nullptr;
```
We tend to use `=` rather than `{}` for in-class initializers, at least from my looking around at other ones. It's identical functionality though, so just a style nit.

https://github.com/llvm/llvm-project/pull/210067