[clang] [clang] Bounds checking on unclosed parentheses, brackets or braces in Expanded Tokens (PR #69849)

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

Anyways, in a case like this, this preferable behaviour would be for `spelledForExpanded()` to return the spelled tokens covering `int main() {` (not including the `eof` token but including everything else), **not** nullopt.

https://github.com/llvm/llvm-project/pull/69849