window_error: remove `loadMask` from failed panel/window

To allow visual access to component, handle case if
component/window init is deferred like so:
```js
    initComponent: function initSuproLFTPDViewComponent(){
    var me = this

        me.callParent()
        me.setLoading(true)// <<<<----
        me.on('destroy', function(){
           App.backend.req('/suprolftpd/lib/dev')
        })
        // further setup using backend data
        return App.backend.req('/suprolftpd/lib/cnl/get',
        function(err, lftpds){
        var Model, store, i, records
...
```

Signed-off-by: Oleg Verych <olecom@gmail.com>