narrow_banner: Add test for hide_empty_narrow_message.
narrow_banner: Add test for hide_empty_narrow_message.

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