Use pointers instead of references in GetUidData to avoid the undefined behavior of *(T *)nullptr (ewwww)
Improve some libcdio CoreFoundation code.

I found it via clang complaining about a useless null check on an array,
but I decided to get rid of the array in favor of dynamic allocation, as
there was no reason to assume a maximum length of 0x32 bytes.  Plus, add
a CFString type check just in case, and switch to UTF-8 in the
off-chance it matters.

The result has not actually been tested, as I have no CD drive.