DosGlob: Don’t use the magic 2nd arg to glob

DosGlob: Don’t use the magic 2nd arg to glob

Use the address of the glob op instead.

This argument is going away, because it is undocumented, unused on
CPAN outside of the core, and may get in the way of allowing glob() to
be overridden properly.

Another reason is that File::DosGlob leaks memory, because a glob op
freed before iteration has finished will leave File::DosGlob still
holding on to the remainder of the list of files.  The easiest way to
fix that will involve using an op address instead of a special index,
so there will be no reason to keep it.