[clang] [analyzer] Mention possibility of underflow in array overflow errors (PR #84201)

[Balázs Kéri via cfe-commits]

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@@ -83,6 +83,8 @@ class StateUpdateReporter {
     AssumedUpperBound = UpperBoundVal;
   }
 
+  bool assumedNonNegative() { return AssumedNonNegative; }
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balazske wrote:

This should be called `getAssumedNonNegative` or `hasAssumedNonNegative` (but the naming rule looks not very strict for this case)?

https://github.com/llvm/llvm-project/pull/84201