Fix #35677, #35525: cycles viewport not updating properly in some situations.

Revision 56883 broke a mechanism where cycles tags itself to be updated later
while it is busy.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57306 954f8c5b-7b00-dc11-b283-0030488c597c
Fix related to #35681: avoid some unnecessary cycles updated when using exclude
render layers.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57307 954f8c5b-7b00-dc11-b283-0030488c597c