dracut-install falls over if sysroot argument end with `/`

[kubiko]

Describe the bug
when --sysrootdir argument is used, internal buffer handling gets confused

Distribution used
Ubuntu 24.04

Dracut version
2, but also present when compiled from master

Init system
Ubuntu 24.04

To Reproduce
Simpliest is to pass `--sysrootdir /'
e.g.

mkdir /tmp/test.dracut
/usr/lib/dracut/dracut-install --debug -D /tmp/test.dracut --ldd -r / /usr/bin/true

as result, marformed lib symbolic link is created, lib -> /sr/lib

Expected behavior
install completes without error with correct directory structure in the destination directory created

Additional context
None