Fix crash when diagnostic is emit with invalid location,
but with attached valid ranges. Diagnostic can contain
invalid location, but SourceManager attached to it still
can be valid, use it in such case or fallback to known
SourceManager.
Fixes: #64602
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D157649
(cherry picked from commit efd44f80a5a8194b9fe26ff3244ce702cd8dab73)