[analyzer] Fix a bug where PathDiagnosticLocation did not generate a valid range and add asserts to check validity of locations early on. Ignore invalid ranges in PathDiagnosticPiece (they could be added by checker writers).

Addresses radar://10124836 and radar://radar10102244.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@140218 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed