Blender Git Loki

Fix T42303 Icons lost after loading window

The issue here is that if no matching winid is found, we destroy all
windows and their context with them. This will also delete the OpenGL
textures associated with the initial context, thus we lose the icons.
This patch makes sure a window is always kept for later so the initial
context does not get lost.

Thanks to Campbell and Ton for the discussion on the issue.