Knob::evaluateValueChange: fix bug introduced in d27f94b523e634698022ff08cdf142814322c516 (easy to find now that there are no more inverse values, like isSignificant and isInsignificant)
EffectInstance::evaluate: fix bug signaled by static analysis (knob may be NULL)
Project::stackEvaluateRequest: fix misnamed variable (wasBeginCalled actually meant that begin was called before entering the function, but was called within the function)