GSDX: Disable a buggy vertex tracer optimisation in GetTextureMinMax (produces a rectangle with a negative dimension leaving it still empty after the follow block which is likely a hack itself).  Fixes textures in Kingdom Hearts 2's tron stage.

git-svn-id: http://pcsx2.googlecode.com/svn/trunk@5610 96395faa-99c1-11dd-bbfe-3dabce05a288