ui/gtk: Only try to initialize EGL/X11 if GtkGlArea failed

The commit referenced below changed the logic by causing the gtk-egl
backend to be initialized regardless of whether GtkGlArea initialization
succeeded. This causes eglInitialize to crash in Wayland systems without
XWayland.

This patch restores the previous logic.

Fixes: 4c70280 ("ui/gtk: use GtkGlArea on wayland only")
Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Message-id: 20180507134237.14996-1-tomeu.vizoso@collabora.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

ui/gtk.c

@@ -2484,7 +2484,7 @@ static void early_gtk_display_init(DisplayOptions *opts)
         if (GDK_IS_WAYLAND_DISPLAY(gdk_display_get_default())) {
             gtk_use_gl_area = true;
             gtk_gl_area_init();
-        }
+        } else
 #endif
         {
             gtk_egl_init();