ui/gtk: force realization of drawing area

Fixes the GL context creation from a widget that isn't yet realized (in
a hidden tab for example).

Resolves:
https://gitlab.com/qemu-project/qemu/-/issues/1727

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Antonio Caggiano <quic_acaggian@quicinc.com>
Message-Id: <20231017111642.1155545-1-marcandre.lureau@redhat.com>
(cherry picked from commit 565f85a)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

ui/gtk.c

@@ -2317,6 +2317,7 @@ static void gtk_display_init(DisplayState *ds, DisplayOptions *opts)
     GdkDisplay *window_display;
     GtkIconTheme *theme;
     char *dir;
+    int idx;
 
     if (!gtkinit) {
         fprintf(stderr, "gtk initialization failed\n");
@@ -2379,6 +2380,15 @@ static void gtk_display_init(DisplayState *ds, DisplayOptions *opts)
     gtk_container_add(GTK_CONTAINER(s->window), s->vbox);
 
     gtk_widget_show_all(s->window);
+
+    for (idx = 0;; idx++) {
+        QemuConsole *con = qemu_console_lookup_by_index(idx);
+        if (!con) {
+            break;
+        }
+        gtk_widget_realize(s->vc[idx].gfx.drawing_area);
+    }
+
     if (opts->u.gtk.has_show_menubar &&
         !opts->u.gtk.show_menubar) {
         gtk_widget_hide(s->menu_bar);