[Nested widgets] Error thrown when pasting widget with nested editable into nested editable

[Olek Nowodziński]

Part of #10931.

There's an error thrown while pasting block Image2 widget into Simple Box

Uncaught TypeError: Cannot read property 'filter' of undefined widget/plugin.js:2116

followed by an avalanche of errors during the navigation.

[Jakub Ś]

NOTE: filter is just first of properties. If you then click in editor content area you get information about removeClass and equals being unavailable as well (focusedEditable is undefined).

[Piotrek Koszuliński]

Wow. This is a tricky issue. The problem is caused by editor.insertHtml() trying to select nested editable after pasting widget rather than selecting it as we do later. It create a erroneous situation in which we try to put selection to nested editable of not yet initialised widget. We'll either need to fix insertHtml() or leave a hack that detects and handles this situation in widget system.

I will first check if insertHtml() can be fixed.

[Piotrek Koszuliński]

Pushed ​branch:t/12008. I fixed insertHtml() what fixed this case. Note - fix does not cover IE8. Very likely we'll not support nested widgets in IE8 for some time. I'll add failing test to regressions.

[Olek Nowodziński]

Pushed µCommit with fixed code-style.

[Piotrek Koszuliński]

Fixed on major with ​git:c17735f.