[mutter/wayland] cursor-tracker: Add a comment about what previous is

[Jasper St. Pierre <jstpierre src gnome org>]

commit 11de01741cee8fec904ccfff44ab1bdd8a8938f5
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Mon Mar 31 14:16:54 2014 -0400

    cursor-tracker: Add a comment about what previous is
    
    It confused me a bit.

 src/core/meta-cursor-tracker.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/core/meta-cursor-tracker.c b/src/core/meta-cursor-tracker.c
index cdf389f..7480ed6 100644
--- a/src/core/meta-cursor-tracker.c
+++ b/src/core/meta-cursor-tracker.c
@@ -949,6 +949,7 @@ meta_cursor_tracker_queue_redraw (MetaCursorTracker *tracker)
 
   g_assert (meta_is_wayland_compositor ());
 
+  /* Clear the location the cursor was at before, if we need to. */
   if (tracker->previous_is_valid)
     {
       clip.x = tracker->previous_rect.x;