window.removeEventListener called too soon if site uses message events for something else

[SpeedoPasanen]

Hi,

this is a quick fix so I'll just post it here instead of making a pull request :)

My site uses messaging for other purposes, so sometimes file picker stops working because someone else sends a message, and filemanager stops listening. On the PHP8 branch, in plugin.min.js line 104:

window.removeEventListener('message', receiveMessage, false);
if (event.data.sender === 'responsivefilemanager') {
    callback(event.data.url);
}

... should be changed to:

if (event.data.sender === 'responsivefilemanager') {
    window.removeEventListener('message', receiveMessage, false);
    callback(event.data.url);
}

Thanks!