[PATCH] allow sync-mailbox when no messages are visible

[Jason Uhlenkott <jasonuhl@xxxxxxxxxxxx>]

This makes sync-mailbox work even if the current limited view is
empty.

Index: mutt/curs_main.c
===================================================================
--- mutt.orig/curs_main.c       2008-04-06 18:45:57.000000000 -0700
+++ mutt/curs_main.c    2008-04-06 18:46:01.000000000 -0700
@@ -1003,7 +1003,6 @@
          break;
 
        CHECK_MSGCOUNT;
-        CHECK_VISIBLE;
        CHECK_READONLY;
        {
          int oldvcount = Context->vcount;