GdkGLContext: Add display property

We need to use this in the code path where we make the context
non-current during destroy, because at that point the window
could be destroyed and gdk_window_get_display() would return
NULL.

gdk/wayland/gdkglcontext-wayland.c

@@ -365,6 +365,7 @@ gdk_wayland_window_create_gl_context (GdkWindow     *window,
             g_print ("Created EGL context[%p]\n", ctx));
 
   context = g_object_new (GDK_TYPE_WAYLAND_GL_CONTEXT,
+                          "display", display,
                           "window", window,
                           "profile", profile,
                           "shared-context", share,