crash on textDocument/didOpen if a previously watched text document is requested again

[repelliuss]

sending following request twice crashes the server

[Trace - 06:35:41 PM] Sending notification 'textDocument/didOpen'.
Params: {
  "textDocument": {
    "uri": "file:///c%3A/foo/foo.hlsli",
    "languageId": "hlsl",
    "version": 0,
    "text": "..."
  }
}

with

thread 'main' panicked at shader-language-server\src\server\server_file_cache.rs:799:17:
File file:///C:/Develop/mango-verse-beta/Engine/Source/Shaders/Native/Source/Shaders/Atmosphere/Bruneton.hlsli already watched as main.
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[antaalt]

Indeed, there is an assert to check this as it should not happen, maybe we can be more relaxed about it