Fix a Far::StencilTablesFactory crash bug on 'perfect' topology
Fix a Far::StencilTablesFactory crash bug on 'perfect' topology

Torii (and other planar topologies) are made entirely of regular b-spline patches and do not
generate sub-patches through adaptive isolation: we need to make sure that we construct
stencil tables with singular stencils for the coarse vertices instead of returning empty
tables (and crash in the limit stencils factory)

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