vc4: Avoid negative scissor caused by no intersection

This fixes 6 tests that were crashing on VC4 since
EGL_KHR_swap_buffers_with_damage was enabled.

dEQP-EGL.functional.swap_buffers_with_damage.*.buffer_age_render

Cc: 20.2 <mesa-stable>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6976>
1 file changed