[connman] ofono: set_property_calls table was destroyed too early

It should be kept alive until after we made all the calls that can call us back.
Otherwise we may end up accessing hashtable that has already been destroyed.
[connman] fix crash and report error properly

connect_service() calls __connman_service_connect() which may in turn call
reply_pending() which unrefs service->pending and sets it to NULL. Therefore,
connect_service() needs to check service->pending for NULL prior to calling
dbus_message_unref() on it.

Also, __connman_error_failed() expects a positive error code.
Merge pull request #87 from monich/service_pending_crash

service: fix crash and report error properly
Merge pull request #86 from monich/remove_modem_crash

ofono: set_property_calls table was destroyed too early