Fix people section vanishing on 'clear cache'

Stop the client first

Fixes https://github.com/vector-im/riot-web/issues/3610

src/components/structures/UserSettings.js

@@ -443,6 +443,7 @@ module.exports = React.createClass({
     _onClearCacheClicked: function() {
         if (!PlatformPeg.get()) return;
 
+        MatrixClientPeg.get().stopClient();
         MatrixClientPeg.get().store.deleteAllData().done(() => {
             PlatformPeg.get().reload();
         });