[cff] Make the `*curveto' operators more tolerant. * src/cff/cf2intrp.c (cf2_interpT2CharString): The opcodes `vvcurveto', `hhcurveto', `vhcurveto', and `hvcurveto' all iterate, pulling values off the stack until the stack is exhausted. Implicitly the stack must be a multiple (or for subtly different behaviour) a multiple plus a specific number of extra values deep. If that's not the case, enforce it (as the old code did).