UPS Rest API: handling cases where a single service is returned by UPS

[fballiano]

Everything is explained in #4043

Fixes #4043

[kiatng]

Ref issue #4043, the property "RatedShipment" is usually an array, but if there is only one item in it, then it is an object.

isset($arr['Service']) looks for the key "Service" in $arr (JSON object) and return true if it's truthy. If the key doesn't exist, it returns false.

@F1Red5 proposal is_string(array_key_first($arr)) returns true on "RatedShipment" originally is a JSON object, it doesn't check that the object has the property "Service".

Based on this, I think testing "RatedShipment" for an object is may be better as it doesn't assume what keys $arr has. But may be it's necessary to check for the key "Service", so I don't know. I defer the decision to the PR author @fballiano.

[fballiano]

the code object of this PR parses a maximum of 10 records, I would never trade readability and understandability of code for such a minor improvement in this context. if we were parsing millions then we should be having this talk, but having this talk now for this specific thing, in my opinion, doesn't make any sense. we should have this lever of participation with the other million things we should be doing instead of wasting energy for this.

I've personally tested all of the UPS implementation, @iamniels tested that this PR works for him (because he submitted it actually) so I really cannot understand all of this chat.

[kiatng]

@fballiano thanks for the clarification and your efforts!