i915 and i965: Prevent invalid framebuffer usage
When a surfaceless context is in use, driDrawablePriv might be NULL, so needs to be checked before calling dri2InvalidateDrawable. Same for read calls.
Fixes #778 (closed)
When a surfaceless context is in use, driDrawablePriv might be NULL, so needs to be checked before calling dri2InvalidateDrawable. Same for read calls.
Fixes #778 (closed)