Diffusion Krita 27f648a75b65

Fixed a bug on undoing removal of last assistant

Authored by tusooaw on May 28 2019, 8:11 AM.

Description

Fixed a bug on undoing removal of last assistant

Undoing the removal of the last assistant will not make the
removed assistant show up again. This is due to the removal
of the last assistant in KisPaintingAssistantsDecoration
will setVisible(false), but the undo command has yet to
revert this.

This commit involves API changes in
KisPaintingAssistantsDecoration.