libfdisk: ignore misaligned optimal I/O size

libfdisk: ignore misaligned optimal I/O size

For example:

 # modprobe scsi_debug dev_size_mb=1000 opt_blks=65535 physblk_exp=3

creates a disk with:

 Sector size (logical/physical): 512 bytes / 4096 bytes
 I/O size (minimum/optimal): 4096 bytes / 33553920 bytes

where 33553920 % 4096 != 0, it means that use Optimal I/O size to
align partition results that partition is not aligned to physical
sector boundary.

Reported-by: Tom Yan <tom.ty89@gmail.com>
Signed-off-by: Karel Zak <kzak@redhat.com>