fixed a small code flaw in Mailbox.c as reported in PR#28898

mail/xmailbox/distinfo

@@ -1,7 +1,8 @@
-$NetBSD: distinfo,v 1.3 2005/02/24 09:59:30 agc Exp $
+$NetBSD: distinfo,v 1.4 2005/03/04 15:31:42 schwarz Exp $
 
 SHA1 (xmailbox-2.5.tar.gz) = 5a213b7551c1d288bb5d5eb16b857c24ac72be38
 RMD160 (xmailbox-2.5.tar.gz) = 9a3c1e3fae890bdb84da09cca8357ceba9705b25
 Size (xmailbox-2.5.tar.gz) = 43535 bytes
 SHA1 (patch-aa) = 31682497caef92bed7b0cde4c1ace990079938af
 SHA1 (patch-ab) = de5e0dc8ec927827c156d61a1e4291ddaa6973dc
+SHA1 (patch-ac) = d449b1f13f5cedb04d7390e80e9d720b17f77730

mail/xmailbox/patches/patch-ac

@@ -0,0 +1,11 @@
+--- Mailbox.c.orig	2005-03-04 15:58:13.000000000 +0100
++++ Mailbox.c	2005-03-04 15:58:52.000000000 +0100
+@@ -276,7 +276,7 @@
+     return (XtGetGC ((Widget) w, valuemask, &xgcv));
+ }
+ 
+-int zombiekiller()
++void zombiekiller()
+ {
+ 	int	status;
+