[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:

> As @vbvictor mentioned, we should add a test for this. We have [lit tests](https://llvm.org/docs/CommandGuide/lit.html) like [this](https://searchfox.org/llvm/source/clang-tools-extra/clangd/test/crash-parse.test) for this purpose, where you can provide clangd some LSP requests as input, and check that its output is what we expect (e.g. in this case, we could check for our log message).

Alright, I'll create a new test file for this?

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