[gtk+/gtk-3-22] gdk-wayland: Do not leak dummy 1x1 surface on every draw

[Daniel Elstner <daniel src gnome org>]

commit a57630b30cab3d1f2762988fa6c66a0c936bc08a
Author: Daniel Elstner <daniel kitta gmail com>
Date:   Tue Sep 26 21:13:40 2017 +0200

    gdk-wayland: Do not leak dummy 1x1 surface on every draw
    
    When using EGL, neither leak nor re-create the dummy 1x1 Cairo
    surface every time gdk_wayland_window_ensure_cairo_surface()
    is called.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=775126

 gdk/wayland/gdkwindow-wayland.c |   15 +++++++++------
 1 files changed, 9 insertions(+), 6 deletions(-)
---
diff --git a/gdk/wayland/gdkwindow-wayland.c b/gdk/wayland/gdkwindow-wayland.c
index cde31e3..e25c782 100644
--- a/gdk/wayland/gdkwindow-wayland.c
+++ b/gdk/wayland/gdkwindow-wayland.c
@@ -840,13 +840,16 @@ gdk_wayland_window_ensure_cairo_surface (GdkWindow *window)
     {
       if (impl->staging_cairo_surface &&
           _gdk_wayland_is_shm_surface (impl->staging_cairo_surface))
-        cairo_surface_destroy (impl->staging_cairo_surface);
+        g_clear_pointer (&impl->staging_cairo_surface, cairo_surface_destroy);
 
-      impl->staging_cairo_surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
-                                                                impl->scale,
-                                                                impl->scale);
-      cairo_surface_set_device_scale (impl->staging_cairo_surface,
-                                      impl->scale, impl->scale);
+      if (!impl->staging_cairo_surface)
+        {
+          impl->staging_cairo_surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
+                                                                    impl->scale,
+                                                                    impl->scale);
+          cairo_surface_set_device_scale (impl->staging_cairo_surface,
+                                          impl->scale, impl->scale);
+        }
     }
   else if (!impl->staging_cairo_surface)
     {