recorder: Call cairo_surface_mark_dirty on the cursor surface

Cairo surfaces have to be marked dirty after directly accessing
them.

This fixes the problem of the cursor not being in the recordings.

src/shell-recorder.c

@@ -412,6 +412,8 @@ recorder_fetch_cursor_image (ShellRecorder *recorder)
   for (i = 0; i < cursor_image->height; i++)
     for (j = 0; j < cursor_image->width; j++)
       *(guint32 *)(data + i * stride + 4 * j) = cursor_image->pixels[i * cursor_image->width + j];
+
+  cairo_surface_mark_dirty (recorder->cursor_image);
 }
 
 /* Overlay the cursor image on the frame. We draw the cursor image