fix add resource with no instance

Signed-off-by: Trial97 <alexandru.tripon97@gmail.com>
(cherry picked from commit c5efe081b4ff9ec81b882e6deabcbfc5be269329)

launcher/ui/MainWindow.cpp

@@ -1027,6 +1027,14 @@ void MainWindow::processURLs(QList<QUrl> urls)
             continue;
         }
 
+        if (APPLICATION->instances()->count() <= 0) {
+            CustomMessageBox::selectable(this, tr("No instance!"),
+                                         tr("No instance available to add the resource to.\nPlease create a new instance before "
+                                            "attempting to install this resource again."),
+                                         QMessageBox::Critical)
+                ->show();
+            continue;
+        }
         ImportResourceDialog dlg(localFileName, type, this);
 
         if (dlg.exec() != QDialog::Accepted)