Bugfix for nullptr check by klocwork

Klocwork static check:
Pointer from call to function `DebugLoc::operator DILocation *() const `
may be NULL and will be dereference in function `printExtendedName```
Patch by Shengchen Kan (skan)
Differential Revision: https://reviews.llvm.org/D61715

llvm-svn: 360317