Call XInitThreads early enough

Call XInitThreads early enough

We need to call XInitThreads before anyone tries XOpenDisplay or
something, and XInitThreads itself is not re-entrant, so call it before
we start LibVLC. This only "fixes" Xlib with VLC. Other LibVLC users
need to do something similar themselves. LibVLC cannot do it. Other
application may have already connected to X before it starts LibVLC.