list_to_streams: Use simpler if statement flow.
list_to_streams: Use simpler if statement flow.

Since each if statement just raises an exception if triggered,
removing the else blocks makes the logic more readable.

kou/zulip,andersk/zulip,eeshangarg/zulip,zulip/zulip,rht/zulip,zulip/zulip,zulip/zulip,andersk/zulip,zulip/zulip,kou/zulip,eeshangarg/zulip,andersk/zulip,rht/zulip,eeshangarg/zulip,kou/zulip,eeshangarg/zulip,rht/zulip,rht/zulip,eeshangarg/zulip,kou/zulip,zulip/zulip,zulip/zulip,rht/zulip,rht/zulip,eeshangarg/zulip,andersk/zulip,kou/zulip,kou/zulip,rht/zulip,andersk/zulip,andersk/zulip,eeshangarg/zulip,andersk/zulip,kou/zulip,zulip/zulip