Previously `newHeight` was updated in parallel, so that applying
operation at height H did not imply successful TreeApply() for H-1.
And because we have no context in TreeUpdateLastSyncHeight(), invalid
starting height could be written if the context was canceled.
In this commit we return the new height only if all operations were
successfully applied.
Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
1. In redo() we save the old state.
2. If we do redo() for the same operation twice, the old state will be
overritten with the new one.
3. This in turn affects undo() and subsequent isAncestor() check.
Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
