Junio Hamano pointed out that there is an implicit assumption in pretty
much all the code calling has_dos_drive_prefix(): it assumes that the
DOS drive prefix is always two bytes long.
While this assumption is pretty safe, we can still make the code more
readable and less error-prone by introducing a function that skips the
DOS drive prefix safely.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
ffcd315739