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.)

doc/fixes3-7-0.txt

@@ -1457,6 +1457,10 @@ adding command line 'nethack --usage' broke 'nethack -u name' (however,
 being hit by a big monster and getting knockback effect could send hero out
 	of a shop (or into its "free spot") while carrying unpaid goods;
 	robbery wasn't noticed until hero eventually moved to a different spot
+hallucination of objects incorrectly included generic objects as candidates
+	for what objects looked like; if an object had its dknown flag set,
+	formatting a generic object in its place was unreliable (Null pointer
+	deference prior to static analyzer fix, odd fake name "generic" after)
 
 curses: 'msg_window' option wasn't functional for curses unless the binary
 	also included tty support

include/display.h

@@ -180,9 +180,11 @@
  * random_object()
  *
  * Respectively return a random monster or object.
+ * random_object() won't return STRANGE_OBJECT or the generic objects.
+ * -/+ MAXOCLASSES is used to skip it and them.
  */
-#define random_monster(rng) rng(NUMMONS)
-#define random_object(rng) (rng(NUM_OBJECTS - 1) + 1)
+#define random_monster(rng) ((*rng)(NUMMONS))
+#define random_object(rng) ((*rng)(NUM_OBJECTS - MAXOCLASSES) + MAXOCLASSES)
 
 /*
  * what_obj()

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;