Handle context.warden being nil

[aericson]

Before #4433, from_context returned PassThruWarden when context.warden was nil.

This could happen, for example, when #warden falls back to query.warden which could have been initialized with warden: nil.

[rmosolgo]

I'm definitely game for this change, but I'd like to include a test so I don't accidentally break it in the future. Do mind adding one? If not, I'll circle back and add one soon.

[aericson]

I'm definitely game for this change, but I'd like to include a test so I don't accidentally break it in the future. Do mind adding one? If not, I'll circle back and add one soon.

Should have done it before 😅. I've now added it on warden_spec.rb. Do you have a better suggestion for it?

[rmosolgo]

Awesome, thanks!