Currently we appear to treat an empty search string the same as regular ones, which is confusing since on 'enter' it shows an empty search box and jumps to eg. the full selection of streams, leaving the search box blank.

Solutions may be to treat 'enter' with an empty string:

• the same as 'esc', ie. that an empty string search should cancel the search (and return somewhere?)
• the same as 'esc', but moving explicitly into the stream list at some point?
• as doing nothing: checking if the box contains a valid value before allowing enter to do anything, ie. locking the user into the box until they press esc explicitly

This is marked as a good first issue since I expect it to be fairly straightforward, but we may need to discuss different approaches in the #zulip-terminal stream on chat.zulip.org first.