Bug 742229 - "pixels" entries get added to unit menus on each popup

_gimp_unit_store_sync_units(): don't trigger a sync of newly added
units if we encounter GIMP_UNIT_PERCENT, it has a special value that
is always larger than any other unit. All unit menus containing
"percent" were broken the same way.

libgimpwidgets/gimpunitstore.c

@@ -923,7 +923,8 @@ _gimp_unit_store_sync_units (GimpUnitStore *store)
                           GIMP_UNIT_STORE_UNIT, &unit,
                           -1);
 
-      if (unit > private->synced_unit)
+      if (unit != GIMP_UNIT_PERCENT &&
+          unit > private->synced_unit)
         {
           GtkTreePath *path;
 
@@ -933,6 +934,5 @@ _gimp_unit_store_sync_units (GimpUnitStore *store)
         }
     }
 
-
   private->synced_unit = gimp_unit_get_number_of_units () - 1;
 }