Bail out early if we don't have a valid source range

Author: DougGregor

lib/Sema/TypeCheckAvailability.cpp

@@ -4058,6 +4058,9 @@ class ExprAvailabilityWalker : public BaseDiagnosticWalker {
 
 static void suggestUnsafeOnEnclosingDecl(
     SourceRange referenceRange, const DeclContext *referenceDC) {
+  if (referenceRange.isInvalid())
+    return;
+
   ASTContext &ctx = referenceDC->getASTContext();
   std::optional<ASTNode> versionCheckNode;
   const Decl *memberLevelDecl = nullptr;