Fix warning caused by removing command-line handling

This will be readded as soon as we support xmpp: URIs.

src/main.rs

@@ -50,7 +50,6 @@ fn main() {
 
     let app = adw::Application::builder()
         .application_id("fr.linkmauve.XmppClient")
-        .flags(gio::ApplicationFlags::HANDLES_COMMAND_LINE)
         .build();
 
     let tabs_store = gio::ListStore::new::<Tab>();
@@ -73,7 +72,7 @@ fn main() {
         }
     });
 
-    app.connect_startup(move |app| {
+    app.connect_activate(move |app| {
         let win = window::MainWindow::new(app);
 
         let action_close = gio::ActionEntry::builder("close")