Skip drawing to a zero-area render target TRAC #12172 This also generates a GL_INVALID_FRAMEBUFFER_OPERATION error when glClear attempt to operate on an invalid or incomplete framebuffer. Signed-off-by: Shannon Woods Signed-off-by: Daniel Koch Author: Nicolas Capens git-svn-id: https://angleproject.googlecode.com/svn/trunk@241 736b8ea6-26fd-11df-bfd4-992fa37f6226