generic object fix

When hallucinating, random object selection for objects was including
the new generic objects.  It was already excluding 'strange object'
by using 'rn2(NUM_OBJECTS - 1) + 1' to skip objects[0]; changing that
to be 'rn2(NUM_OBJECTS - MAXOCLASSES) + MAXOCLASSES' will skip the
first 18 objects, 'strange object' plus the 17 generic objects.

(I'm trying to convince myself that there's no off-by-1 or off-by-N
error and think I've succeeded.)

src/pager.c

@@ -332,10 +332,11 @@ look_at_object(
 }
 
 static void
-look_at_monster(char *buf,
-                char *monbuf, /* buf: output, monbuf: optional output */
-                struct monst *mtmp,
-                coordxy x, coordxy y)
+look_at_monster(
+    char *buf,
+    char *monbuf, /* buf: output, monbuf: optional output */
+    struct monst *mtmp,
+    coordxy x, coordxy y)
 {
     char *name, monnambuf[BUFSZ], healthbuf[BUFSZ];
     boolean accurate = !Hallucination;