In all games, rs_write_room_reference() stored -1 for a nonexistent
room, but rs_read_room_reference() did not check for out-of-bounds
values, leading to pointers to rooms[-1], which sometimes caused
crashes. rs_read_room_reference() has now been modified to use NULL
instead.
Some of the games required further changes to replace NULL with the
pointer to the actual room. Others are capable of handling NULL for
objects not in any room.
A buffer called curpurch, which stores a description of an item in a
trading post which the player might be interested in, was only 15
bytes. It was overflowing into oldrp, a room pointer, leading to
segfaults. The size of curpurch has been increased to LINELEN*2,
which matches the size of prbuf, which is returned by inv_name and
then strcpy()'d to curpurch. As long as nothing overflows prbuf it
should be safe now.
NOTE that this breaks savefile compatibility.
