libfdisk: (dos) ignore incomplete EBR for non-wholedisk

libfdisk: (dos) ignore incomplete EBR for non-wholedisk

The logical partitions are defined by a chain of extended partitions,
with the beginning of the chain located on the whole disk device.

If a user runs "fdisk --list /dev/sda4", libfdisk cannot calculate proper
offsets for the items in the chain, resulting in the following error
message:

 Failed to read extended partition table (offset=22528): Invalid argument

This error message may confuse users and is unnecessary when fdisk is
used in list-only mode (--list option). It would be sufficient to only
print the content of the partition without the error message and not
continue to the next item in the chain.

However, in write mode (without --list), the error message will still
be displayed as it is potentially dangerous to edit the EBR table.

Addresses: https://issues.redhat.com/browse/RHEL-59867
Signed-off-by: Karel Zak <kzak@redhat.com>