cli: characters typed before CLI is initialised are ignored

Before the bubbline change, I used to be able to type characters before the CLI was initialised and have the CLI recognise them.

Now, before the `demo@127.0.0.1:26257/defaultdb>` is displayed, all my characters before that go to a black hole. Example (typing asdf):
```
$ ./cockroach demo --empty
asdf
#
# Welcome to the CockroachDB demo database!
#
# You are connected to a temporary, in-memory CockroachDB cluster of 1 node.
...
#
# Enter \? for a brief introduction.
#
demo@127.0.0.1:26257/defaultdb>
```

It is worth noting using `CI=1 ./cockroach demo --empty` fixes this issue.

Jira issue: CRDB-22389

Epic CRDB-23743