codec/zvbi: Do not follow dead color-links

If a color-key is requested check the stored nav-link to be in the valid page
range before following it. This avoids unexpected disappearance of the
teletext overlay if a color-link does not exist or is not yet loaded.
Signed-off-by: Julian Scheel <julian@jusst.de>
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/codec/zvbi.c

@@ -661,32 +661,37 @@ static int RequestPage( vlc_object_t *p_this, char const *psz_cmd,
 {
     decoder_sys_t *p_sys = p_data;
     VLC_UNUSED(p_this); VLC_UNUSED(psz_cmd); VLC_UNUSED(oldval);
+    int want_navlink = -1;
 
     vlc_mutex_lock( &p_sys->lock );
     switch( newval.i_int )
     {
         case ZVBI_KEY_RED:
-            p_sys->i_wanted_page = vbi_bcd2dec( p_sys->nav_link[0].pgno );
-            p_sys->i_wanted_subpage = p_sys->nav_link[0].subno;
+            want_navlink = 0;
             break;
         case ZVBI_KEY_GREEN:
-            p_sys->i_wanted_page = vbi_bcd2dec( p_sys->nav_link[1].pgno );
-            p_sys->i_wanted_subpage = p_sys->nav_link[1].subno;
+            want_navlink = 1;
             break;
         case ZVBI_KEY_YELLOW:
-            p_sys->i_wanted_page = vbi_bcd2dec( p_sys->nav_link[2].pgno );
-            p_sys->i_wanted_subpage = p_sys->nav_link[2].subno;
+            want_navlink = 2;
             break;
         case ZVBI_KEY_BLUE:
-            p_sys->i_wanted_page = vbi_bcd2dec( p_sys->nav_link[3].pgno );
-            p_sys->i_wanted_subpage = p_sys->nav_link[3].subno;
+            want_navlink = 3;
             break;
         case ZVBI_KEY_INDEX:
-            p_sys->i_wanted_page = vbi_bcd2dec( p_sys->nav_link[5].pgno ); /* #4 is SKIPPED */
-            p_sys->i_wanted_subpage = p_sys->nav_link[5].subno;
+            want_navlink = 5; /* #4 is SKIPPED */
             break;
     }
-    if( newval.i_int > 0 && newval.i_int < 999 )
+
+    if (want_navlink > -1)
+    {
+        int page = vbi_bcd2dec( p_sys->nav_link[want_navlink].pgno );
+        if (page > 0 && page < 999) {
+            p_sys->i_wanted_page = page;
+            p_sys->i_wanted_subpage = p_sys->nav_link[want_navlink].subno;
+        }
+    }
+    else if( newval.i_int > 0 && newval.i_int < 999 )
     {
         p_sys->i_wanted_page = newval.i_int;
         p_sys->i_wanted_subpage = VBI_ANY_SUBNO;