relent on silver bell usage...

Allow a hero in silver-hating form to ring the Bell of Opening when
on the vibrating square so be able to perform the invocation ritual.
But only at that location and only if the stairs aren't there yet.

This is about on par with being able to read the Book of the Dead
while blind although that isn't limited to a specific location.

doc/fixes37.0

@@ -1,4 +1,4 @@
-$NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.234 $ $NHDT-Date: 1593309675 2020/06/28 02:01:15 $
+$NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.235 $ $NHDT-Date: 1593611274 2020/07/01 13:47:54 $
 
 General Fixes and Modified Features
 -----------------------------------
@@ -199,6 +199,8 @@ attempting to read a novel while blind reported "you can't read the mystic
 don't let life draining reduce a monster's max HP below its level + 1
 report "<Mon> expires" rather than "<Mon> dies" if polymorphed hero kills a
 	non-living monster (golem, vortex) with life drain (vampire bite)
+allow hero in silver-hating form to ring the silver bell but only if on/over
+	the vibrating square
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository

src/artifact.c

@@ -1,4 +1,4 @@
-/* NetHack 3.6	artifact.c	$NHDT-Date: 1593306896 2020/06/28 01:14:56 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.157 $ */
+/* NetHack 3.6	artifact.c	$NHDT-Date: 1593611274 2020/07/01 13:47:54 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.158 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2013. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -1948,6 +1948,12 @@ boolean loseit;    /* whether to drop it if hero can longer touch it */
 {
     struct obj *obj = *objp;
 
+    /* allow hero in silver-hating form to try to perform invocation ritual */
+    if (obj->otyp == BELL_OF_OPENING
+        && invocation_pos(u.ux, u.uy) && !On_stairs(u.ux, u.uy)) {
+        return 1;
+    }
+
     if (touch_artifact(obj, &g.youmonst)) {
         char buf[BUFSZ];
         int dmg = 0, tmp;