Bug fix #34943

With extreme narrow scaled editors, the slider/mask code in View3d could deliver
zero sized or invalid window matrices.

Needs confirmation from Sergey if it works :)




git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56129 954f8c5b-7b00-dc11-b283-0030488c597c