busybox ed jumps line on insert

[karlsebal]

Busybox‘s implementation of `ed` skips a line when inserting. It will insert the first line before and all subsequent lines after the line addressed.

gnu ed implementation behaves like expected:

```
$ ed
i
one
two
three
four
five
.
,p
one
two
three
four
five
1
one
i
ione
itwo
ithree
ifive
.
,p
ione
itwo
ithree
ifive
one
two
three
four
five
Q
```

The lines »ione« through »ifive« are inserted before the line »one«. But busybox’s behaviour differs:

```
$ busybox ed
: i
one
two
three
four
five
.
: ,p
one
two
three
four
five
: 1
one
: i
ione
itwo
ithree
ifour
ifive
.
: ,p
ione
one
itwo
ithree
ifour
ifive
two
three
four
five
: q
Really quit? y
```

The line »ione« is inserted before »one« and the lines »itwo« through »ifive« are appended after »one«. However, `append` works as expected.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: busybox (not installed)
ProcVersionSignature: Ubuntu 5.4.0-81.91-generic 5.4.128
Uname: Linux 5.4.0-81-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.18
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: Regolith:GNOME-Flashback:GNOME
Date: Sun Aug 29 08:27:55 2021
InstallationDate: Installed on 2020-10-14 (318 days ago)
InstallationMedia: Regolith 20.04.0 1.4.1 LTS amd64 (20200511)
SourcePackage: busybox
UpgradeStatus: No upgrade log present (probably fresh install)