FIx #37005: Mask tool + "Area" Brush Mapping + "Anchored" Stroke = crash

Was caused by area normal calvultion using undo nodes to get coords
from and undo nodes does not contain coords whe using mask tool.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@60747 954f8c5b-7b00-dc11-b283-0030488c597c