demux: ts: don't clear temporary program list on SET_GROUP (fix #19434)

otherwise we don't know which program is selected
maybe core might feedback this one day

modules/demux/mpeg/ts.c

@@ -1087,7 +1087,7 @@ static int Control( demux_t *p_demux, int i_query, va_list args )
 
             p_sys->b_default_selection = false;
         }
-        else
+        else if( !p_sys->b_default_selection )
         {
             ARRAY_RESET( p_sys->programs );
             p_sys->seltype = PROGRAM_AUTO_DEFAULT;