[clang] [clang][NFC] Avoid potential null dereferences (PR #127017)

[via cfe-commits]

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@@ -314,6 +314,7 @@ void MacOSKeychainAPIChecker::checkPreStmt(const CallExpr *CE,
     RegionArgIsBad = true;
   }
 
+  assert(ArgSM);
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schittir wrote:

Thank you!

https://github.com/llvm/llvm-project/pull/127017