Fix Undocked Outliner & multiple window crashes (#11004).

Fix Undocked Outliner & multiple window crashes (#11004).

There are more independent crashes occuring in this scenario and this
fix targets only one of them, in particular the one in which different
window's outliner sends outliner command to a wrong window. The fix
itself gives an option for lfun to know which window it belongs to.

https://www.mail-archive.com/lyx-devel@lists.lyx.org/msg203619.html