Bug 14496

input:
```
$ cat << EOF | sort -k2rn -s
a 1
b 2
c 1
d 2
EOF
```

result with coreutils and toybox:
```
b 2
d 2
a 1
c 1
```

result with busybox:

```
d 2
b 2
c 1
a 1
```

whereas it should return the lines a, b, c, d according to the documented behavior of the 'stable' (`-s`) parameter, but instead returns d, b, c, a. It should reverse the order of the second column only and keep the first in the same order provided via stdin according to the `-r` flag as the implementation from GNU coreutils does.