ibfdisk: (gpt) allow to maximize partition

ibfdisk: (gpt) allow to maximize partition

enlarge second partition:

	# echo ',+' | ./sfdisk -N2 /dev/sdb
	...
	Disk /dev/sdb: 100 MiB, 104857600 bytes, 204800 sectors

	Old situation:
	Device     Start   End Sectors Size Type
	/dev/sdb1   2048 22527   20480  10M Linux filesystem
	/dev/sdb2  22528 43007   20480  10M Linux filesystem

	New situation:
	Device     Start    End Sectors Size Type
	/dev/sdb1   2048  22527   20480  10M Linux filesystem
	/dev/sdb2  22528 204766  182239  89M Linux filesystem

Signed-off-by: Karel Zak <kzak@redhat.com>