Remove check for zero focal length in BA cost functor
Remove check for zero focal length in BA cost functor

This check is actually redundant, because empty intrinsics
will have focal length of 1.0, which means original comment
about BundleIntrinsics was not truth.

It is possible that external user will send focal length of
zero to be refined, but blender prevents this from happening.

rgkoo/libmv-blender,rgkoo/libmv-blender,petertsoi/libmv,SoylentGraham/libmv,rgkoo/libmv-blender,SoylentGraham/libmv,petertsoi/libmv,petertsoi/libmv,rgkoo/libmv-blender,petertsoi/libmv,SoylentGraham/libmv,SoylentGraham/libmv,rgkoo/libmv-blender