Dir#tell leads to segfaults in Dir#read on win32
rb_w32_telldir calculates the position on each call by repeatedly calling move_to_next_entry.
This increases dirp->loc each time and leads to segfaults in rb_w32_readdir when reading dirp->bits because dirp->loc can be larger than allowed. Simply returning dirp->loc in rb_w32_telldir and zeroing it in rb_w32_rewinddir should suffice.
This bug seemed to never got introduced into the 1.9 branch.