vi: avoid touching a new file with ZZ when no editing has been done

vi: avoid touching a new file with ZZ when no editing has been done

This is the behaviour observed with standard vim and busybox vi of at
least 1.22.1.  It was changed with commit "32afd3a vi: some
simplifications" which happened before 1.23.0.

Mistyping filename on command line happens fairly often and it's better
we restore the old behaviour to avoid a few unnecessary flash writes and
sometimes efforts of debugging bugs caused by those unneeded stray
files.

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>