This also 'fixes' RTSP playback crashes (#2742)

You don't want random web pages listing, say, the content of your
hard drive (file/xspf-open://C:/ ?). For debugging purpose, the standard
error from Mozilla is probably better than Javascript anyway, not to
mention that the libvlc logging APi is really brain-damaged.

for the strucure).

deallocated).

Indeed, giving a NULL to var_Change(VLC_VAR_SETSTRING) will lead to a crash the
next time this variable is used.

There are still bugs. At least posx, posy, pos and b_need_update are not
protected properly, but I don't have time.

A corner case occured if the mask were changed during initialization.

Close #2573

As advised on the forum, !/ is the standard separator for JAR protocol.