Fix handling of CreateTemplateParameterList when there is an empty pack

Summary:
When we are creating a ClassTemplateSpecializationDecl in ParseTypeFromDWARF(...) we are not handling the case where variadic pack is empty in the specialization. This patch handles that case and adds a test to prevent future regressions.

Differential Revision: https://reviews.llvm.org/D57363

llvm-svn: 352677