We can take elsid's commit 605cb8d further by avoiding the terrain sync completely in most cases. Currently in changeCellGrid we wait for a new preloading task to ensure the getPagedRefnums for the new active cells have been filled in by object paging. This is usually not necessary because we have already completed a preload in the past containing these active cells. With this PR we remember what we preloaded and skip the terrain sync if it is not needed.