Crash when typing in editor placeholder test

[FilipTokarski]

Type of report

Bug

Provide detailed reproduction steps (if any)

1. Create full-all build in ckeditor4-presets
2. Open test /tests/plugins/editorplaceholder/manual/fullpage
3. Type something

Expected result

No errors in console

Actual result

Uncaught TypeError: Cannot read property '1' of null
    at a.f (ckeditor.js:849)
    at a.e (ckeditor.js:10)
    at a.<anonymous> (ckeditor.js:11)
    at a.CKEDITOR.editor.CKEDITOR.editor.fire (ckeditor.js:13)
    at CKEDITOR.plugins.undo.UndoManager.type (ckeditor.js:1263)
    at CKEDITOR.plugins.undo.NativeEditingHandler.onKeyup (ckeditor.js:1274)
    at $.e (ckeditor.js:10)
    at $.fire (ckeditor.js:11)
    at HTMLBodyElement.<anonymous> (ckeditor.js:69)

Other details

• latest major branch