Reply with {error, closed} instead of {error, illegal_state} on calls…

[kpy3]

… to closed connection

This fixes #932

[kpy3]

5 days no new invalid state so far

[benoitc]

Merged as part of #936, which carries your commit as-is plus a follow-up that scopes the reply to calls with no handler. The catch-all placed ahead of handle_common also shadowed response_headers, get_location, get_protocol, checkin_info and close_socket in the closed state, which broke hackney:location/1. Replying from handle_common's fallback keyed on the state keeps those answering and drops the need for the hackney_pool workaround. Thanks for the fix and the diagnosis.