Accessor function for bvh::num_prims()
Accessor function for bvh::num_prims()

Fixes a "XXX will be initialized before YYY" warning

ukoeln-vis/ctpperf,szellmann/visionaray,ukoeln-vis/ctpperf,szellmann/visionaray,tu500/visionaray,tu500/visionaray