Fix transcript to users without email

packages/rocketchat-livechat/app/client/lib/commands.js

@@ -13,7 +13,8 @@ this.Commands = {
 
 	promptTranscript: function() {
 		if (Livechat.transcript) {
-			let email = Meteor.user().emails[0].address || '';
+			const user = Meteor.user();
+			let email = user.emails && user.emails.length > 0 ? user.emails[0].address : '';
 
 			swal({
 				title: t('Chat_ended'),
@@ -60,4 +61,4 @@ this.Commands = {
 			});
 		}
 	}
-};
+};