fix discussion topic permissions for draft state

when draft state is enabled, it shouldn't grant
reply rights when a topic is closed for comments

test plan:
* create and publish a discussion topic
* close it for comments
* as a student, should not be able to add a reply
 through the api

refs #CNVS-15563

Change-Id: I238f2e8956c9bd3136dfd69db5bb4d63c07102c0
Reviewed-on: https://gerrit.instructure.com/42282
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>