regfio: Return instead of assert for short blocks

Assertions should only be used when there's absolutely no recovery or to verify data structure invariants. In this case the supplied registry hive file may have a malformed block with a size of zero. Such a block should not terminate the whole program.

Signed-off-by: Michael Hanselmann public@hansmi.ch Reviewed-by: Andrew Bartlett abartlet@samba.org