Crop cells only if memorizedRange is bigger than expected range

[tchudyk]

When I added VirtualFlow.visibleCells() listener I'm receiving not ending stream of events, but visible cells list is not changing.
The problem seemed to only affect lists where the cell is higher than the visible area (Maybe related to #80).

VirtualFlow<T, C> view = ...;
//.....
view.visibleCells().addListener(new InvalidationListener() {
    @Override
    public void invalidated(Observable observable) {
        System.out.println("a"); // <--- Not ending stream of events (printing `a`).
    }
});

I think the problem may be in package org.reactfx:reactfx:2.0-M5: MemorizationListImpl.forget(int from, int to)
https://github.com/TomasMikula/ReactFX/blob/537fffdbb2958a77dfbca08b712bb2192862e960/reactfx/src/main/java/org/reactfx/collection/MemoizationList.java#L176

It publish events (memoizedItems.fireRemoveRange(memoChangeFrom, memoRemoved)) even if memoRemoved list is empty.

I'm not sure if this behavior in reactfx is good or wrong, but I found workaround to apply in Flowless in CellListManager.cropTo(...) to forget items only when memorizedRange is bigger then our fromItem-toItem range.

[Jugen]

Hi @tchudyk thanks for looking into this and the PR, much appreciated :-)