(SCT_MAXDEF): Make it equal the maximum sector type, not the maximum

(SCT_MAXDEF): Make it equal the maximum sector type, not the maximum
plus one.  Users changed.  This indirectly fixes off-by-one loop
bounds in budg(), show_sect_build(), show_sect_stats() and
show_sect_capab().  The show bugs were harmless: the loops ran into
the sentinel, which they ignore.  The budg bug was serious: the loop
ran into the entries for SCT_EFFIC.  This lead to a bogus line in the
budget, printing of a null pointer, and doubled sector build cost.
Budget priorities masked this bug until rev. 1.25.