Bug 33221 [UBSAN] segfault with -fsanitize=undefined

There is can be a situation when vptr is not initializing
by constructor of the object, and has a junk data which should
be properly checked, because c++ standard says:

"if default constructor is not specified
16 (7.3) no initialization is performed."

Patch by Denis Khalikov!

Differential Revision: https://reviews.llvm.org/D33712

llvm-svn: 304437