glStencilViewer crash fix #2
glStencilViewer crash fix #2

this change fixes a crash when selecting catmark_hole_test1
in glStencilViewer. If there's a hole limit stencils may not
be found for given limit location, resulting invalid stencil
entries.

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