Fix r_speeds 4 in OpenGL2 renderer
Fix r_nocurves in OpenGL2 renderer

Check r_nocurves in surface cull.
While r_nocurves is enabled, don't use merged surfaces because merged curves would be renderer. (note: surface merging is enabled by r_mergeLeafSurfaces)
Fix r_mergeLightmaps 0 crashing OpenGL2 renderer

tr.fatLightmapStep was 0 and caused modulus division by 0.
Merge remote-tracking branch 'upstream/master'