gst/qtdemux/qtdemux.c: Make compile with Forte compiler, mostly don't do pointer...

gst/qtdemux/qtdemux.c: Make compile with Forte compiler, mostly don't do pointer arithmetic with void pointers (#3626...

Original commit message from CVS:
Patch by: Josep Torra Valles  <josep at fluendo com>
* gst/qtdemux/qtdemux.c: (gst_qtdemux_handle_sink_event),
(next_entry_size), (qtdemux_inflate), (qtdemux_parse_moov),
(qtdemux_parse_tree), (qtdemux_parse_trak), (qtdemux_tag_add_str),
(qtdemux_tag_add_num), (qtdemux_tag_add_date),
(qtdemux_tag_add_gnre):
Make compile with Forte compiler, mostly don't do pointer arithmetic
with void pointers (#362626).