MetaRendererNative: Give EGLDevice backend priority over GBM

With GLVND, whenever we have both Mesa's and NVIDIA's drives installed
in the system, initializing the GBM backend will always succeed,
regardless of what GPU you have on your system.

This is due to GBM's software rendering fallback.

It seems better to initialize the EGLDevice backend first, which will
fail to find a device match when given a non-NVIDIA GPU.

https://bugzilla.gnome.org/show_bug.cgi?id=784272

src/backends/native/meta-renderer-native.c

@@ -2070,16 +2070,21 @@ meta_renderer_native_initable_init (GInitable     *initable,
   GError *egl_device_error = NULL;
 #endif
 
-  if (init_gbm (renderer_native, &gbm_error))
-    return TRUE;
-
 #ifdef HAVE_EGL_DEVICE
+  /* Try to initialize the EGLDevice backend first. Whenever we use a
+   * non-NVIDIA GPU, the EGLDevice enumeration function won't find a match, and
+   * we'll fall back to GBM (which will always succeed as it has a software
+   * rendering fallback)
+   */
   if (init_egl_device (renderer_native, &egl_device_error))
+    return TRUE;
+#endif
+
+  if (init_gbm (renderer_native, &gbm_error))
     {
-      g_error_free (gbm_error);
+      g_error_free (egl_device_error);
       return TRUE;
     }
-#endif
 
   g_set_error (error, G_IO_ERROR,
                G_IO_ERROR_FAILED,