Error when client_id is not valid

While reviewing the authentication process of the application i noticed that if an invalid `auth_client_id` query parameter is used the application will crash, ex: https://dwylauth.herokuapp.com/?auth_client_id=42


This is due to the error returns by Field not being caught in the rescue part of the code:
https://github.com/dwyl/auth/blob/3a9d68720c02d2a8bdec33ffd8b70c35a4e5289a/lib/auth/apikey.ex#L46-L56

The `ArgumentError` and `ArithmeticError` are managed but not `MatchError`.

Instead of catching individual errors we can catch them all together:
```
def decode_decrypt(key) do
try do
key |> Base58.decode() |> Fields.AES.decrypt() |> String.to_integer()
rescue
_ -> 0
end
end
```
The app will then able to return a nice error page: