EEwsConnection: Release queue lock as soon as possible in ews_next_request()
EEwsConnection: Release queue lock as soon as possible in ews_next_request()

This could cause a deadlock when other thread cancels an ongoing
request (the ews_next_request() thread inside the e_ews_connection_utils_prepare_message())
and the ews_cancel_request() is called as the callback to the GCancellable::cancelled
signal.

GNOME/evolution-ews,GNOME/evolution-ews