Fix of T36285, I just invalidate projection matrix when a camera switch
to viewport mode, because we need to rewrite the projection matrix in
RenderFrame.
It worked with old blender version because when you use viewport render
one camera is added in the camera list and initialize its projection
matrix for the first time. But when we used several cameras + viewport
for splitscreen we had issues.
Reviewers: dfelinto, hg1, ben2610, lordloki, moguri
Reviewed By: moguri
Projects: #game_rendering, #game_engine
Differential Revision: https://developer.blender.org/D1202
f5648f6db9