i956: Make state dependency of SF on drawbuffer bounds match Mesa's.

Noticed while debugging a weird 1D FBO testcase that left its existing
viewport and projection matrix in place when switching drawbuffers.  Didn't
fix the testcase, though.
(cherry picked from commit 3a521d84ecc646fcc65fa3fe7c5f1fdbdebe8bc2)
1 file changed