Fix #35292: edge slide slow with big image in image editor. Avoid redrawing the
image editor during slide like other operators, instant feedback can be nice but
is not so important here and we don't have notifiers fine grained enough to avoid
full redraws.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56671 954f8c5b-7b00-dc11-b283-0030488c597c