Fix #1426674 - Don't create a history item if no finalization is needed.
Fix #1426674 - Don't create a history item if no finalization is needed.

This works around issues where new history items could be created in the
process of undoing, since setting the active layer forces tools to
commit their work.

A proper fix is to figure out a better alternative to having the curve
tool commit its work whenever the current layer/document is changed (see
bug #1425222)

Mailaender/Pinta,Mailaender/Pinta,Fenex/Pinta,PintaProject/Pinta,Fenex/Pinta,PintaProject/Pinta,jakeclawson/Pinta,PintaProject/Pinta,jakeclawson/Pinta