Remember we were trying to accept an invite

When the user was on an invite page and clicked the sign up/sign in
buttons, remember that invite so we can show it again after they're
done signing up/in.

https://github.com/vector-im/riot-web/issues/9816

src/components/views/rooms/RoomPreviewBar.js

@@ -1,6 +1,7 @@
 /*
 Copyright 2015, 2016 OpenMarket Ltd
 Copyright 2017 Vector Creations Ltd
+Copyright 2019 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -57,6 +58,9 @@ module.exports = React.createClass({
         // For third party invites, information passed about the room out-of-band
         oobData: PropTypes.object,
 
+        // For third party invites, a URL for a 3pid invite signing service
+        signUrl: PropTypes.string,
+
         // A standard client/server API error object. If supplied, indicates that the
         // caller was unable to fetch details about the room for the given reason.
         error: PropTypes.object,
@@ -228,12 +232,25 @@ module.exports = React.createClass({
         return memberContent.membership === "invite" && memberContent.is_direct;
     },
 
+    _makeScreenAfterLogin() {
+        return {
+            screen: 'room',
+            params: {
+                email: this.props.invitedEmail,
+                signurl: this.props.signUrl,
+                room_name: this.props.oobData.room_name,
+                room_avatar_url: this.props.oobData.avatarUrl,
+                inviter_name: this.props.oobData.inviterName,
+            }
+        };
+    },
+
     onLoginClick: function() {
-        dis.dispatch({ action: 'start_login' });
+        dis.dispatch({ action: 'start_login', screenAfterLogin: this._makeScreenAfterLogin() });
     },
 
     onRegisterClick: function() {
-        dis.dispatch({ action: 'start_registration' });
+        dis.dispatch({ action: 'start_registration', screenAfterLogin: this._makeScreenAfterLogin() });
     },
 
     render: function() {