Fix null pointer dereference
Merge branch 'master' of github.com:Unvanquished/Unvanquished
Change RE_SetColorGrading to use the renderer command list

It is not efficient to make OpenGL calls from the main thread with smp enabled
Use R_SyncRenderThread in more places
Reduce the number of calls to GLimp_SetCurrentContext()

GLimp_FrontEndSleep only needs to block until the renderer thread is finished, it does not need to acquire the OpenGL context.
Fix crash with SMP enabled