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

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

Do you understand from this stack trace what is actually segfaulting, e.g. what variable that we're trying to dereference is null? It's not immediately clear to me.

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