app_voicemail: Fix compile breaking in app_voicemail with IMAP_STORAGE.

There is a leftover "assert" in app_voicemail/__messagecount that references 
variables that don't exist.  This causes the compile to fail when 
--enable-dev-mode and IMAP_STORAGE are selected.

This patch removes the assert.

Tested-by: George Joseph

Review: https://reviewboard.asterisk.org/r/4461/
........

Merged revisions 432484 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/13@432485 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_voicemail.c

@@ -2446,7 +2446,6 @@ static int __messagecount(const char *context, const char *mailbox, const char *
 		free_user(vmu);
 		return -1;
 	}
-	ast_assert(msgnum < vms->msg_array_max);
 	/* check if someone is accessing this box right now... */
 	vms_p = get_vm_state_by_imapuser(vmu->imapuser, 1);