fix [#34658] GreasePencil eraser deletes strokes through geometry, surfacemode

add depth check to grease pencil eraser when xray option is disabled.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55588 954f8c5b-7b00-dc11-b283-0030488c597c