1.5.8 removed ability to auth as client

[mcauser]

For Google Maps APIs Premium users, the client parameter is still used.
https://developers.google.com/maps/documentation/javascript/get-api-key#client-id

You can authenticate with either an api key or client id.
https://developers.google.com/maps/documentation/javascript/get-api-key#clientID-features

client param removed in #537

[mcauser]

For those authenticating as a client, the key param is not required.

When passing in both client id and a blank key, it throws an InvalidKey warning:
&client=gme-xxx&key=&libraries=geometry...

It would be great if either the client= or key= params could be appended only when needed.