[gimp] app: another copy/paste error broke moving in GimpToolHandleGrid

[Michael Natterer <mitch src gnome org>]

commit 77d516b588ceb20424aa584528d41931310e43d1
Author: Michael Natterer <mitch gimp org>
Date:   Mon Jun 19 23:45:35 2017 +0200

    app: another copy/paste error broke moving in GimpToolHandleGrid

 app/display/gimptoolhandlegrid.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/app/display/gimptoolhandlegrid.c b/app/display/gimptoolhandlegrid.c
index 39e7422..1d7358b 100644
--- a/app/display/gimptoolhandlegrid.c
+++ b/app/display/gimptoolhandlegrid.c
@@ -739,7 +739,7 @@ gimp_tool_handle_grid_motion (GimpToolWidget   *widget,
               /* move */
               for (i = 0; i < 4; i++)
                 {
-                  newpos_x[i] = oldpos_x[i] + diff_y;
+                  newpos_x[i] = oldpos_x[i] + diff_x;
                   newpos_y[i] = oldpos_y[i] + diff_y;
                 }
               break;