Fix race condition in notifyVisibilityChange

Add isRunning() check before sending notifications to the language
client to prevent "Client is not running" errors in test environments
where the client may not have fully started yet.

Co-authored-by: cklin <1418580+cklin@users.noreply.github.com>

Author: Copilot

extensions/ql-vscode/src/language-support/language-client.ts

@@ -45,6 +45,10 @@ export class CodeQLLanguageClient extends LanguageClient {
   }
 
   notifyVisibilityChange(editors: readonly TextEditor[]) {
+    // Only send notification if the language client is running to avoid race conditions
+    if (!this.isRunning()) {
+      return;
+    }
     const files = editors
       .filter((e) => e.document.uri.scheme === "file")
       .map((e) => e.document.uri.toString());