wayland: Fix xdg-popup crash

We need to remove the destroy listener when we delete a pixmap or it
leaves an invalid node on the signal list.

src/bin/e_pixmap.c

@@ -209,6 +209,11 @@ _e_pixmap_free(E_Pixmap *cp)
       case E_PIXMAP_TYPE_WL:
 #ifdef HAVE_WAYLAND
         _e_pixmap_wayland_image_clear(cp);
+        if (cp->buffer_destroy_listener.notify)
+          {
+             wl_list_remove(&cp->buffer_destroy_listener.link);
+             cp->buffer_destroy_listener.notify = NULL;
+          }
 #endif
         break;
       default: