1) Reset the build when adding potential dirties to the list to ensure it isn't trying to kill off a dirty entry that it's passed by.
2) mSaveIntermediates = true; causes leakage even with all this. still tracking that end.
3) Need to remove a dead tile whether there's new data to replace it with or not. Empty tiles are an entirely possible case. Even a probable one if you have high verticality in a level.
4) Likewise you don't want to re-feed the same geometry list for a given tile in case the conditions have changed.
5) If no vertcount then clear all geometry entries. (that one might be paranoia)
Many instances where we would create a object via a new call, and then check that it was non-null.
This is redundant, as if we ever were in a situation where new failed, we'd be crashing left and right already, so the additional check is wasted processing.
A lot of instances where some function args are not actually modified in any way, meaning that it is better for performance to convert them into const references. This prevents an additional copy, which can help performance.
