consider: Clean up recovery from an impossible error

Drop the unhelpful message to the player, and fail the command.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>

src/lib/commands/cons.c

@@ -90,10 +90,9 @@ cons(void)
 	rv = postpone(&ltc);
 	break;
     default:
-	pr("Bad operation %c from cons_choose; get help!\n", ltc.op);
+	CANT_REACH();
-	break;
+	return RET_SYN;
-    };
+    }
-
     return rv;
 }