Avoid invalid memory reference when 1st arg of path-build is ""

[Jarhmander]

Avoid invalid memory reference when 1st arg of path-build is ""

Before:

> (path-build "" "a")
Exception: invalid memory reference.  Some debugging context lost
Type (debug) to enter the debugger.

After:

> (path-build "" "a")
"a"

Code was simplified a bit at some places to exploit the new changes, but without changing existing behavior.

[burgerrg]

Thanks for finding this! There's another definition of path-build in s/reboot.ss that may need to be updated as well.

[Jarhmander]

Thanks for finding this! There's another definition of path-build in s/reboot.ss that may need to be updated as well.

Thanks!

For the occurrence in s/reboot.ss, I didn't fully understand why this (re?)definition is here, and I just assumed that this script worked correctly in normal circumstances, and since this path-build function is not exported, it could be left alone. I nevertheless modified it to act like the one in 6.ss.

[burgerrg]

I think reboot.ss is loaded by older versions of Chez Scheme, so it's good to have it updated.

Please also add a subsection in the release notes under bugs fixed about this. Thanks!

[burgerrg]

Thank you!