Avoid end partition overlap when resizing extended partition (#678831)

When resizing an extended partition, a problem can occur with MiB
alignment wherein the requested end sector could be less than the end
sector of the last logical partition.  This would be an invalid
geometry because all the logical partitions must be wholly contained
within the extended partition.

Check for this situation and if found then set requested end for
the extended partition to the end of the last logical partition.

Closes Bug #678831 - Partition End Overlap when Resizing Extended
                     Partition