fix #H4706 - non-zero hit points for poison death

For "the poison was deadly" against hero, hit points were set to -1
(which gets displayed as 0 when shown) but the status lines weren't
being updated, so stale positive HP value was visible during final
disclosure.

src/attrib.c

@@ -272,6 +272,7 @@ boolean thrown_weapon; /* thrown weapons are less deadly */
     if (i == 0 && typ != A_CHA) {
         /* instant kill */
         u.uhp = -1;
+        context.botl = TRUE;
         pline_The("poison was deadly...");
     } else if (i > 5) {
         /* HP damage; more likely--but less severe--with missiles */