Image dialog: JavaScript error (invalid argument)

[Wiktor Walc]

It can be reproduced on the demo page. The problem is caused by the "%25" character in the file name.

Steps to reproduce

• Open the Image dialog
• Paste the following in the URL field: /images/Test%25Image.jpg
• Click "Ok" to close the dialog
• Result: an error occurs, the image is not inserted into the document.

Invalid argument.  _source/com/dom/element.js, line 987 character 5

var standard = function( name, value )
{
	this.$.setAttribute( name, value ); // <-- line 987
	return this;
};

[Wiktor Walc]

Looks like a dup of #5256