lost ball and chain (trunk only)

Saving the game while punished, not carrying the attached ball,
and while swallowed by a purple worm resulted in losing the
ball and chain.

Since the required information was not being written to the
save file at all, I couldn't come up with a clean way to do this
for the branch, and preserve save file format. I could think
of lots of kludgy ways to do it (insert ball and chain into
the hero's inventory prior to saving, and remove it on restore, etc.)

src/save.c

@@ -352,6 +352,10 @@ register int fd, mode;
 		uball->nobj = uchain;
 		uchain->nobj = (struct obj *)0;
 		saveobjchn(fd, uball, mode);
+	} else {
+		int minusone = -1;
+		if (perform_bwrite(mode))
+		    bwrite(fd, (genericptr_t) &minusone, sizeof(int));
 	}
 
 	saveobjchn(fd, migrating_objs, mode);