zsh: fix completion when docker output only has the header line
zsh: fix completion when docker output only has the header line

Unfortunately, `(f)` aka `(ps:\n:)` flag will not create an array when
there is only one line. The subsequent use of indexes will then affect
the string. This leads to `docker rmi <tab>` to complete on the header
line instead of nothing.

Therefore, for each use of `(f)`, we ensure that we have an extra new
line to be sure we get an array.

Credit to @povesteam for the original report and fix in #27373.

Signed-off-by: Vincent Bernat <87e1f221a672a14a323e57bb65eaea19d3ed3804@bernat.im>

redpanda/cli,e11137/cli,cpuguy83/cli,redpanda/cli,ashfall/cli,dnephin/cli,allencloud/cli,e11137/cli,docker/cli,ashfall/cli,riyazdf/cli,Zebrilee/cli,thaJeztah/cli,riyazdf/cli,cpuguy83/cli,allencloud/cli,dnephin/cli,thaJeztah/cli,docker/cli,Zebrilee/cli