If the input to 'disklabel' (non -i) referenced a partition two or more
larger than that permitted by npartitions it would error out with 'bad
partition name' (and the option given to re-edit if -e). If a partition one
larger was used it would be dropped from the disklabel with a warning and the
label written anyway! The (off by one) check for a bad partition name was
against npartitions anyway, rather than MAXPARTITIONS. npartitions was just
read from the disklabel and could have been set to an arbitrary value.
Given 'disklabel -i' sets npartitions automatically, make the normal case
check partition names against MAXPARTITIONS, and if necessary increase
npartitions to the size needed to hold the last partition used.
While here remove two 'write only' uses of a 'part' variable.
cb52ff7f22