If an uninitialized or user supplied Socket is in the freeSockets list
of the Agent it would automatically attempt to run
._handle.asyncReset(), but would throw from those not existing. Guard
against that by first checking that they exist.
PR-URL: https://github.com/nodejs/node/pull/14419
Fixes: https://github.com/nodejs/node/issues/13539
Refs: https://github.com/nodejs/node/issues/13352
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
