Fix a splicing bug in FarMultiMeshFactory.
Fix a splicing bug in FarMultiMeshFactory.

* the number of split vertices has to be taken into account when splicing vertex valence table.
* followed patch descriptor iterator api changes.

shengfuintel/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,jcowles/OpenSubdiv,c64kernal/OpenSubdiv,poljere/OpenSubdiv,jcowles/OpenSubdiv,takahito-tejima/OpenSubdiv,xldeveloper/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,anshuarya/OpenSubdiv,lookup1980/OpenSubdiv,takahito-tejima/OpenSubdiv,c64kernal/OpenSubdiv,nyotis/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,poljere/OpenSubdiv,lookup1980/OpenSubdiv,nyotis/OpenSubdiv,shengfuintel/OpenSubdiv,xldeveloper/OpenSubdiv,c64kernal/OpenSubdiv,nyotis/OpenSubdiv,lookup1980/OpenSubdiv,xldeveloper/OpenSubdiv,anshuarya/OpenSubdiv,poljere/OpenSubdiv,takahito-tejima/OpenSubdiv-exp,jcowles/OpenSubdiv,anshuarya/OpenSubdiv,takahito-tejima/OpenSubdiv,shengfuintel/OpenSubdiv