util.paseto: Do strict type check in pae() function
Fixes a test failure on Lua 5.4 where ipairs("") does not produce an
error.
For full information on our dependencies, version requirements, and
where to find them, see https://prosody.im/doc/depends
If you have luarocks available on your platform, install the following:
- luaexpat
- luasocket
- luafilesystem
- luasec