[Edge] Calling `setData` on editor initialization breaks AC in specific cases

[f1ames]

See https://github.com/cksource/new-websites/issues/252 for detailed description of the whole issue.

---

The problem may occur when editor with a11ychecker enabled is initialized like

var editor = CKEDITOR.replace( 'editor', config ); // Nothing special just `extraPlugins: 'a11ychecker'`
editor.on( 'instanceReady', function( evt ) {
    evt.editor.setData( 'Some sample html...' );
} );

After clicking on a11ychecker toolbar button the error is thrown

It happens only for built version of a11ychecker on Edge browser.

Initializing CKEditor on container with html inside does not cause the error. Also deferring setData call like

editor.on( 'instanceReady', function( evt ) {
    setTimeout( function() {
        evt.editor.setData( 'Some sample html...' );
    }, 0 );    
} );

solves the issue. Calling setData after editor instance (with html inside) is properly initialized does not break editor so it is not the issue with only setData method but probably some race condition case.