Fix invalid check of m_precedenceOpCount (#298)

The conditional m_precedenceOpCount >= 0 was always true because m_precendenceOpCount is an unsigned type. Update the conditional to simply be true and rely on a break statement in the loop. Although this member variable used to be a signed type, in practice, the value was never less than 0.

How changes were validated:
Manual. Unit tests pass locally.

src/CalcManager/Header Files/CalcEngine.h

@@ -129,6 +129,7 @@ private:
 
 private:
     void ProcessCommandWorker(OpCode wParam);
+    void ResolveHighestPrecedenceOperation();
     void HandleErrorCommand(OpCode idc);
     void HandleMaxDigitsReached();
     void DisplayNum(void);