Ignore invalid file URIs from LSP

[xJonathanLEI]

This PR changes a call to unwrap() to match. Currently the editor crashes when the LSP publishes diagnostics with an unsupported URI. With this PR it simply ignores them.

Submitting this patch because the Cairo language server crashes Helix when it sends a file URI like vfs://xxxxxx where vfs refers to the internal in-memory file system of the Cairo language server.

I'm not sure if this is considered a bug of the Cairo lang server as I don't know for sure if schemes other than file is allowed. But in any case I think we shouldn't panic here.

[pascalkuthe]

I do think this is a bug in the Cairo LS as the uri is expected to refer to a valid file (otherwise the notification is useless). Howber the LSP standard is pretty vaque and only states that the uri fieldust.ne parsed as a valid URI but not as a valid FILE uri:

Many of the interfaces contain fields that correspond to the URI of a document. For clarity, the type of such a field is declared as a DocumentUri. Over the wire, it will still be transferred as a string, but this guarantees that the contents of that string can be parsed as a valid URI.

I think being defensive is good here (easy fix for a panic) especially as buggy and non standard compliant LSPs are sadly not that rare.

LGTM 👍