[9.x] Fixes HTTP::pool response when a URL returns a null status code

[sulemaanhamza]

This PR fixes the bug reported by sfilzek.

When we try to use HTTP::pool with a URL having an expired certificate, Guzzle returns a RequestException with a null response. I've added an extra check to make sure if the guzzle response is not null then populateResponse otherwise returns the exception.

[shinsenter]

@taylorotwell
I encountered a similar error as above, but the returned result was not a RequestException but a ConnectException. I think it would be best to replace the RequestException of the following code snippet with TransferException:
https://github.com/sulemaanhamza/framework/blob/20f8658355c5b1c843a61c1cdfa249f7da515841/src/Illuminate/Http/Client/PendingRequest.php#L791