zvbi: Use the "initial page" as signaled by the TS demuxer.

This way the TS demux can create multiple tracks that will take you straight to the subtitles, program listings etc.
(cherry picked from commit 344612b3)

modules/codec/zvbi.c

@@ -197,6 +197,16 @@ static int Open( vlc_object_t *p_this )
     var_AddCallback( p_dec, "vbi-page",
                      RequestPage, p_sys );
 
+    /* Check if the Teletext track has a known "initial page". */
+    if( p_sys->i_wanted_page == 100 && p_dec->fmt_in.subs.dvb.i_id != -1 )
+    {
+        int i_wanted_magazine = p_dec->fmt_in.subs.dvb.i_id >> 16;
+        if( i_wanted_magazine == 0 )
+            i_wanted_magazine = 8;
+        p_sys->i_wanted_page = vbi_bcd2dec(p_dec->fmt_in.subs.dvb.i_id & 0xff);
+        p_sys->i_wanted_page += 100*i_wanted_magazine;
+    }
+
     p_sys->b_opaque = var_CreateGetBool( p_dec, "vbi-opaque" );
     var_AddCallback( p_dec, "vbi-opaque", Opaque, p_sys );