When an expected-* directive uses the @unknown location specifier, the
associated ExpectedDiag record has an invalid (null) SMLoc as its
fileLoc. If the expected diagnostic is never produced, emitError() is
called to report the unmatched expectation, but it unconditionally
constructs an SMRange from fileLoc, triggering a null-pointer
dereference (UBSan) and an assertion failure in SMRange's constructor
which requires both endpoints to have equal validity.
Fix by guarding the SMRange construction with a fileLoc.isValid() check.
When fileLoc is invalid, call PrintMessage without a source range.
Fixes#163343
Assisted-by: Claude Code
055322c38a