Blender Git Loki

Fix T76970: Unneccessary update calls viewport

Due to recent changes clicks in the node editor would trigger a
depsgraph update resulting in too many redraws. This patch limits
the updates to when workbench shown in texture mode in any visible
screen.

There are still cases where too many updates are created. For example when
there are a Cycles render viewport and a Workbench texture viewport on the
same screen.

This fix is meant as a workaround. The actual fix should add a mechanism
to the depsgraph and the viewports should check if they need to be redrawn.

Reviewed By: Brecht van Lommel

Differential Revision: https://developer.blender.org/D7830