BUG/MEDIUM: lua: Don't crash in hlua_lua2arg_check on failure

In hlua_lua2arg_check(), on failure, before calling free_argp(), make
sure to always mark the failed argument as ARGT_STOP. We only want to
free argument prior to that point, because we did not allocate the
strings after this one, and so we don't want to free them.

This should be backported up to 2.2.

src/hlua.c

@@ -1101,6 +1101,7 @@ __LJMP int hlua_lua2arg_check(lua_State *L, int first, struct arg *argp,
 	return 0;
 
   error:
+	argp[idx].type = ARGT_STOP;
 	free_args(argp);
 	WILL_LJMP(luaL_argerror(L, first + idx, msg));
 	return 0; /* Never reached */