Fix code scanning alert no. 71

[arvindshmicrosoft]

Fix for https://github.com/microsoft/SQLCallStackResolver/security/code-scanning/71

In general, to fix a constant condition that is always true/false because of local control-flow, remove the redundant condition and keep only the behavior that always happens when that point in the code is reached. Here, by the time we reach line 238 we are already inside if (!resWasCached) { ... }, and resWasCached is never reassigned, so if (!resWasCached) at line 238 is always true. The intended logic is still to guard the cache write with a check against the current dictionary contents, not to re-check the original resWasCached flag. Therefore, the minimal change is to remove the inner if (!resWasCached) wrapper and let the writer-lock section always run when the outer if (!resWasCached) is taken.

Concretely, in Engine/StackResolver.cs, inside ProcessFrameModuleOffset, replace:

238:                 if (!resWasCached) {    // we only need to add to cache if it was not already cached.
239:                     this.rwLockCachedSymbols.AcquireWriterLock(-1);
240:                     if (!this.cachedSymbols.ContainsKey(symKey)) this.cachedSymbols.Add(symKey, result);
241:                     this.rwLockCachedSymbols.ReleaseWriterLock();
242:                 }

with:

238:                 this.rwLockCachedSymbols.AcquireWriterLock(-1);
239:                 if (!this.cachedSymbols.ContainsKey(symKey)) this.cachedSymbols.Add(symKey, result);
240:                 this.rwLockCachedSymbols.ReleaseWriterLock();

This keeps behavior identical: we still only write to the cache when the original lookup missed (outer if (!resWasCached)), but the inner constant condition is removed. No new methods, imports, or definitions are needed.

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