fix #H7454 - Cleaver vs long worm tails

Cleaver's ability to hit up to three adjacent targets could kill a
long worm and then try to cut it in two.  When this was first reported
I was unable to reproduce it, but this time I've managed to do so.
But not reliably, so it's hard to claim that it's now fixed.  However,
the new report's explanation of why it happens and suggested fix was a
big help.  I had been trying to hit three tail segments, but you need
to attack a segment next to the head, then have Cleaver hit and kill
the head first (50:50 chance depending upon whether current swing is
clockwise or counter).  Worm cutting would be looking at the location
of the targetted segment but there won't be any monster there when the
head dies.  (Cleaver's attack itself already copes the situation where
its 2nd and/or 3rd potential targets aren't there any more by the time
it's ready to try to hit them.)

doc/fixes36.2

@@ -1,4 +1,4 @@
-$NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.282 $ $NHDT-Date: 1553480403 2019/03/25 02:20:03 $
+$NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.283 $ $NHDT-Date: 1553644725 2019/03/26 23:58:45 $
 
 This fixes36.2 file is here to capture information about updates in the 3.6.x
 lineage following the release of 3.6.1 in April 2018. Please note, however,
@@ -396,6 +396,8 @@ status lines' dungeon location field in the elemental planes now shows Earth
 	or Air or Fire or Water instead of generic End Game
 avoid spurious status refresh when hero gains experience while 'showexp' and
 	'showscore' options are off
+using Cleaver to attack a worm tail segment but kill adjacent head first would
+	result in an impossible warning from cutworm
 
 
 Fixes to Post-3.6.1 Problems that Were Exposed Via git Repository