Avoid unref of EEwsConnection in ews_connection_scheduled_cb()
Avoid unref of EEwsConnection in ews_connection_scheduled_cb()

If that's the last reference, then the e_ews_connection_dispose() will try
to wait for the soup_thread, but this is run in soup_thread, thus it cannot
be done and application is aborted on checking for deadlock.

GNOME/evolution-ews,GNOME/evolution-ews