TRAC #12643

IDirect3DDevice9::Clear will fail if asked to clear a buffer that is not present, so we have to be careful what we pass to it.

Signed-off-by: Shannon Woods
Signed-off-by: Daniel Koch

Author:    Andrew Lewycky

git-svn-id: https://angleproject.googlecode.com/svn/trunk@341 736b8ea6-26fd-11df-bfd4-992fa37f6226