Fix a KJS crash on gmail.
The problem was that in some cases, such as event evaluation (which is a function context with callingContext being the globalExec) we would break the chain of active execStates.

That meant we couldn't update them right when moving the stack due to expansion (It also means that they won't get marked sometimes.

Good thing I didn't put in smarter stack code that never puts in things yet --- otherwise it would take 3 days to debug instead of half a day)