libobs: Fix Projectors closing when toggling Always On Top

[liamphmurphy]

Pretty much my first PR ever to a project.

Please let me know of any suggestions or if there is a better way to fix.

Was brought to my attention by bug 0001166 on the tracker.

[jp9000]

I'm assuming you didn't test this on all three primary operating systems. This is safe to do on windows, but not on other operating systems. On macOS for example, if you open the properties window, then set the main window to always on top, then try to close that properties window, the program will crash. This is presumably because way the "always on top" feature works and can be modified varies between operating systems. On some operating systems, such as windows, you can do this safely because internally the Win32 API can change the state with no issues. On other operating systems such as macOS and certain Linux window managers, the entire window hierarchy has to be recreated internally. The macOS crash is probably a bug with Qt, but none-the-less, the dialogs should still be closed on non-windows systems just to be safe.

I'm modifying it with that change then committing.