outgoing_webhook: Simplify error handling logic.
outgoing_webhook: Simplify error handling logic.

Structurally, exception, failure_message, and status_code are mutually
exclusive in how this function is called, and it's best for the
function's flow to represent that.

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