clipproperties: Keyframes added on play bug fixed

Authored by stefanzzz on Jun 26 2017, 8:42 AM.

Description

clipproperties: Keyframes added on play bug fixed

When playing the preview, unintended keyframes were sometimes added. This
happened because changes in the source properties led to changes in spin
button values, which were misinterpreted as user inputs.

Differential Revision: https://phabricator.freedesktop.org/D1770