minor: Update comment for guest subscription access.
minor: Update comment for guest subscription access.

As my comment indicates, I would prefer to handle
this explicitly by raising JsonableError in an
else statement here, but it's not a big deal.

This function can probably be simplified with a
bit of work, mostly on the testing side to make
sure we are covering all edge cases, but that
is out of the scope of my current PR.

kou/zulip,eeshangarg/zulip,rht/zulip,andersk/zulip,hackerkid/zulip,eeshangarg/zulip,zulip/zulip,hackerkid/zulip,andersk/zulip,punchagan/zulip,kou/zulip,rht/zulip,andersk/zulip,andersk/zulip,zulip/zulip,andersk/zulip,kou/zulip,hackerkid/zulip,punchagan/zulip,eeshangarg/zulip,rht/zulip,eeshangarg/zulip,zulip/zulip,andersk/zulip,rht/zulip,eeshangarg/zulip,hackerkid/zulip,punchagan/zulip,rht/zulip,zulip/zulip,hackerkid/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,punchagan/zulip,andersk/zulip,eeshangarg/zulip,zulip/zulip,zulip/zulip,punchagan/zulip,hackerkid/zulip,punchagan/zulip,punchagan/zulip,hackerkid/zulip,rht/zulip,rht/zulip,kou/zulip,kou/zulip,kou/zulip