Fix a crash in DWARFUnit::getInlinedChainForAddress in case of unexpected DWARF information.

In some cases a broken or invalid debug info could cause a crash in DWARFUnit::getInlinedChainForAddress during parsing a chain of in-lined functions. This patch fixes this issue.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D98119