actions: Use transaction.atomic in do_change_logo_source.
actions: Use transaction.atomic in do_change_logo_source.

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