disconnect render() on window change
when the window changes, the node will be deleted, and render()
will access an invalid pointer.
disconnect the render slot when the window change, as it
can't do anything useful until the next updatepaintnode.
Make the managedtexturenode actually do the management, as
textures were never deleted
The bug is easily reproducible without the patch, wasn't
able to reproduce it anymore with it
Reviewers: Plasma, davidedmundson
Reviewed By: Plasma, davidedmundson
Subscribers: davidedmundson, broulik, ngraham, plasma-devel, Frameworks
Differential Revision: https://phabricator.kde.org/D10250