[clang-tools-extra] [clangd] Fix SIGSEGV crash when receiving a textDocument/didOpen request with the URI pointing to a directory (PR #177834)

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dhr412 wrote:

I think its probably the FileEntryRef object (`Val` in frame 0) that has a null internal pointer which is getting dereferenced

https://github.com/llvm/llvm-project/pull/177834