fix "Killed by foo, while paralyzed by a monster"

If the killer and the paralyzer are the same monster, truncate
that to "Killed by a foo, while paralyzed".  When not the same,
spell out the paralyzer's monster type instead of using generic
"monster".  "Killed by a fox, while paralyzed by a ghoul", or
"Killed by a ghoul, while paralyzed by a ghoul" *if* they were
two different ghouls.

src/hack.c

@@ -3020,7 +3020,7 @@ nomul(int nval)
     u.usleep = 0;
     g.multi = nval;
     if (nval == 0)
-        g.multi_reason = NULL;
+        g.multi_reason = NULL, g.multireasonbuf[0] = '\0';
     end_running(TRUE);
 }
 
@@ -3047,7 +3047,7 @@ unmul(const char *msg_override)
     }
     g.nomovemsg = 0;
     u.usleep = 0;
-    g.multi_reason = NULL;
+    g.multi_reason = NULL, g.multireasonbuf[0] = '\0';
     if (g.afternmv) {
         int (*f)(void) = g.afternmv;