Fix a possible crash in IMAP voicemail.

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@80750 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_voicemail.c

@@ -4421,7 +4421,7 @@ static int play_message(struct ast_channel *chan, struct ast_vm_user *vmu, struc
 	mail_fetchstructure (vms->mailstream,vms->msgArray[vms->curmsg],&body);
 	
 	/* We have the body, now we extract the file name of the first attachment. */
-	if (body->nested.part->next && body->nested.part->next->body.parameter->value) {
+	if (body->nested.part && body->nested.part->next && body->nested.part->next->body.parameter->value) {
 		attachedfilefmt = ast_strdupa(body->nested.part->next->body.parameter->value);
 	} else {
 		ast_log(LOG_ERROR, "There is no file attached to this IMAP message.\n");