lang/crystal: unbreak runtime after r507877

$ cat >foo.cr
require "http/client"
HTTP::Client.get "http://api.icndb.com/jokes/1"

$ crystal foo.cr
[warn] event_reinit: forked from the event_loop.
Unhandled exception in spawn: Error reinitializing libevent (Exception)
[warn] event_reinit: forked from the event_loop.
Unhandled exception in spawn: Error reinitializing libevent (Exception)
[warn] event_reinit: forked from the event_loop.
Unhandled exception in spawn: Error reinitializing libevent (Exception)
[warn] event_reinit: forked from the event_loop.
[warn] event_reinit: forked from the event_loop.
[...]

PR: 206355
Reported by: Petr Fischer
Submitted by: Walter Schwarzenfeld
Approved by: Greg V (maintainer)