Fix missing brush cursor redraw for texture paint when no pixels changed in the
image, no images need to be refreshed then but the cursors needs to be redrawn
still. Otherwise it gets stuck, especially annoying in unexpected cases where the
mask has reached the maximum for all pixels in the brush.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56448 954f8c5b-7b00-dc11-b283-0030488c597c