stream_create: Use `switch` instead of multiple `else-if`.
stream_create: Use `switch` instead of multiple `else-if`.

This change was forced by our linter in the previous commit.

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