fix(linux): call gtk_init to fix tauri-apps/tauri#11312

.changes/explicit_gtk_init.md

@@ -0,0 +1,7 @@
+---
+"tao": patch
+---
+
+Explicitly call `gtk::init()` as `gtk::Application::new` does not call it reliably.
+If `gtk::init()` is not called, 'GTK may only be used from the main thread' error can occur later.
+`gtk::init()` checks if already initialized and does nothing if so.

src/platform_impl/linux/event_loop.rs

@@ -215,6 +215,8 @@ impl<T: 'static> EventLoop<T> {
   }
 
   fn new_gtk(app_id: Option<&str>) -> Result<EventLoop<T>, Box<dyn Error>> {
+    // This should be done by gtk::Application::new, but does not work properly
+    gtk::init()?;
     let context = MainContext::default();
     let app = gtk::Application::new(app_id, gio::ApplicationFlags::empty());
     let app_ = app.clone();