Lock offline mode support behind insertion of at least one Minecraft account

Co-Authored-By: Naomi Calabretta <tony0000.ac@gmail.com>

launcher/ui/pages/global/AccountListPage.cpp

@@ -156,6 +156,19 @@ void AccountListPage::on_actionAddMicrosoft_triggered()
 
 void AccountListPage::on_actionAddOffline_triggered()
 {
+    if (!m_accounts->anyAccountIsValid()) {
+        QMessageBox::warning(
+            this,
+            tr("Error"),
+            tr(
+                "You must add a Microsoft or Mojang account that owns Minecraft before you can add an offline account."
+                "<br><br>"
+                "If you have lost your account you can contact Microsoft for support."
+            )
+        );
+        return;
+    }
+
     MinecraftAccountPtr account = OfflineLoginDialog::newAccount(
         this,
         tr("Please enter your desired username to add your offline account.")