Convert 3PID lookup in preview bar to async / await

src/components/views/rooms/RoomPreviewBar.js

@@ -104,21 +104,21 @@ module.exports = React.createClass({
         }
     },
 
-    _checkInvitedEmail: function() {
+    _checkInvitedEmail: async function() {
         // If this is an invite and we've been told what email
         // address was invited, fetch the user's list of Threepids
         // so we can check them against the one that was invited
         if (this.props.inviterName && this.props.invitedEmail) {
             this.setState({busy: true});
-            MatrixClientPeg.get().lookupThreePid(
-                'email', this.props.invitedEmail,
-            ).finally(() => {
-                this.setState({busy: false});
-            }).done((result) => {
+            try {
+                const result = await MatrixClientPeg.get().lookupThreePid(
+                    'email', this.props.invitedEmail,
+                );
                 this.setState({invitedEmailMxid: result.mxid});
-            }, (err) => {
+            } catch (err) {
                 this.setState({threePidFetchError: err});
-            });
+            }
+            this.setState({busy: false});
         }
     },