Fix VSCODE 1683 - HelpCommentReqHdlr crash on GetFile (#850)

Author: rkeithhill

src/PowerShellEditorServices.Protocol/Server/LanguageServer.cs

@@ -1162,7 +1162,15 @@ protected async Task HandleCommentHelpRequest(
            CommentHelpRequestParams requestParams,
            RequestContext<CommentHelpRequestResult> requestContext)
         {
-            ScriptFile scriptFile = this.editorSession.Workspace.GetFile(requestParams.DocumentUri);
+            var result = new CommentHelpRequestResult();
+
+            ScriptFile scriptFile;
+            if (!this.editorSession.Workspace.TryGetFile(requestParams.DocumentUri, out scriptFile))
+            {
+                await requestContext.SendResult(result);
+                return;
+            }
+
             int triggerLine = requestParams.TriggerPosition.Line + 1;
 
             string helpLocation;
@@ -1171,8 +1179,6 @@ protected async Task HandleCommentHelpRequest(
                 triggerLine,
                 out helpLocation);
 
-            var result = new CommentHelpRequestResult();
-
             if (functionDefinitionAst == null)
             {
                 await requestContext.SendResult(result);