When blank, callerid name and number should display "unknown caller" in voicemail

emails.
(Closes issue #13643)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@147997 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_voicemail.c

@@ -2932,7 +2932,8 @@ static void prep_email_sub_vars(struct ast_channel *ast, struct ast_vm_user *vmu
 	pbx_builtin_setvar_helper(ast, "VM_MSGNUM", passdata);
 	pbx_builtin_setvar_helper(ast, "VM_CONTEXT", context);
 	pbx_builtin_setvar_helper(ast, "VM_MAILBOX", mailbox);
-	pbx_builtin_setvar_helper(ast, "VM_CALLERID", ast_callerid_merge(callerid, sizeof(callerid), cidname, cidnum, "Unknown Caller"));
+	pbx_builtin_setvar_helper(ast, "VM_CALLERID", (!ast_strlen_zero(cidname) || !ast_strlen_zero(cidnum)) ?
+		ast_callerid_merge(callerid, sizeof(callerid), cidname, cidnum, NULL) : "an unknown caller");
 	pbx_builtin_setvar_helper(ast, "VM_CIDNAME", (!ast_strlen_zero(cidname) ? cidname : "an unknown caller"));
 	pbx_builtin_setvar_helper(ast, "VM_CIDNUM", (!ast_strlen_zero(cidnum) ? cidnum : "an unknown caller"));
 	pbx_builtin_setvar_helper(ast, "VM_DATE", date);