Always call launchUrlVSCode, error or not (#6780)

This should prevent a repeat of https://github.com/flutter/devtools/issues/6105 if an exception occurs while trying to open the page when embedded inside VS Code.

packages/devtools_app/lib/src/shared/config_specific/launch_url/launch_url.dart

diff --git a/packages/devtools_app/lib/src/shared/config_specific/launch_url/launch_url.dart b/packages/devtools_app/lib/src/shared/config_specific/launch_url/launch_url.dart
index abe8121..cf3b5de 100644
--- a/packages/devtools_app/lib/src/shared/config_specific/launch_url/launch_url.dart
+++ b/packages/devtools_app/lib/src/shared/config_specific/launch_url/launch_url.dart
@@ -12,14 +12,20 @@
 Future<void> launchUrl(String url) async {
   final parsedUrl = Uri.tryParse(url);
 
-  if (parsedUrl != null && await url_launcher.canLaunchUrl(parsedUrl)) {
-    await url_launcher.launchUrl(parsedUrl);
-  } else {
-    notificationService.push('Unable to open $url.');
+  try {
+    if (parsedUrl != null && await url_launcher.canLaunchUrl(parsedUrl)) {
+      await url_launcher.launchUrl(parsedUrl);
+    } else {
+      notificationService.push('Unable to open $url.');
+    }
+  } finally {
+    // Always pass the request up to VS Code because we could fail both silently
+    // (the usual behaviour) or with another error like
+    // "Attempted to call Window.open with a null window"
+    // https://github.com/flutter/devtools/issues/6105.
+    //
+    // In the case where we are not in VS Code, there will be nobody listening
+    // to the postMessage this sends.
+    launchUrlVSCode(url);
   }
-
-  // When embedded in VSCode, url_launcher will silently fail, so we send a
-  // command to DartCode to launch the URL. This will do nothing when not
-  // embedded in VSCode.
-  launchUrlVSCode(url);
 }