Assertion failure in HttpTransact::is_response_valid() when a parent proxy is down. #8366
Description
When testing on a debug master build, a failure to connect to an upstream parent proxy that is down, an assertion crash occurs at HttpTransact::is_response_valid():334. s->current.state is set to BAD_INCOMING_RESPONSE which is not in the list of current.state values accepted in the ink_assert().
In 9.1.x, when a parent is down, the current.state comes in as CONNECTION_CLOSED but in master it's now BAD_COMING_RESPONSE.