[Safari] Can't focus widget's editable

[kkrzton]

Steps to reproduce

Note: this issue appears only on built version of CKEditor.

1. Open ​​http://tests.ckeditor.dev:1030/tests/plugins/widget/manual/block.
2. Focus the Classic editor by clicking on header like Len^na.
3. Focus caption inside first image widget like Image of Lena Söderberg us^ed in many image processing experiments..

Expected result

The editable caption is focusable.

Actual result

Caret jumps to the beginning of the content.

Other details (browser, OS, CKEditor version, installed plugins)

Tested on Safari 10.0.1 (11602.2.14.0.7) and 10.0.1 (12602.2.14.0.7).

Happens only in classic editor, inline editor works fine.

[Marek Lewandowski]

I was able to reproduce it on built version only. Dev version works fine.

[Marek Lewandowski]

I can reproduce it with 4.6.0 so it's not a regression in this release.