mind flayer vs headless target

When a mind flayer scores a hit against a headless target (or worm's
tail), there's a message that says that the attack hits and that the
target is unharmed.  Since an ordinary mind flayer has 3 such attacks
per turn and a master mind flayer has 5, it can become excessively
verbose.

This doesn't eliminate the attacks until a hit fails to do harm, so
ordinary misses still get repeated if they happen first.  Once a
successful hit doesn't do anything, any remaining AT_TENT+AD_DRIN
attacks are silently skipped.  That way feedback isn't as verbose
and mind flayers don't seem to be quite so stupid about using their
tentacles when those won't work.  Unfortunately they need to relearn
the lesson every turn they attack.

src/decl.c

@@ -1,4 +1,4 @@
-/* NetHack 3.6	decl.c	$NHDT-Date: 1593953345 2020/07/05 12:49:05 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.214 $ */
+/* NetHack 3.6	decl.c	$NHDT-Date: 1594730611 2020/07/14 12:43:31 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.215 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Michael Allison, 2009. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -461,9 +461,10 @@ const struct instance_globals g_init = {
     /* makemon.c */
 
     /* mhitm.c */
-    UNDEFINED_VALUE, /* vis */
-    UNDEFINED_VALUE, /* far_noise */
-    UNDEFINED_VALUE, /* noisetime */
+    0L, /* noisetime */
+    FALSE, /* far_noise */
+    FALSE, /* vis */
+    FALSE, /* skipdrin */
 
     /* mhitu.c */
     UNDEFINED_VALUE, /* mhitu_dieroll */