lua: fix vlc.msg.dbg with multiple parameters

(cherry picked from commit 00d43bb27c4c6e3b4dbcd8aa43b3af58536b3c5b)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/misc/lua/libs/messages.c

@@ -54,7 +54,7 @@ static int vlclua_msg_dbg( lua_State *L )
     vlc_object_t *p_this = vlclua_get_this( L );
     int i;
     for( i = 1; i <= i_top; i++ )
-        msg_Dbg( p_this, "%s", luaL_checkstring( L, 1 ) );
+        msg_Dbg( p_this, "%s", luaL_checkstring( L, i ) );
     return 0;
 }