Fix issues with retina screenshots

What does this MR do and why?

Fix issues with retina screenshots

In rich text editor, when pasting a retina screenshot, it showed full sized screenshot, instead of half the size. This was due to multiple issues:

• Buffer was undefined on some devices, and
• width and height were cached in the wrapper. This is now fixed. The bug was introduced in !160357 (merged).

Changelog: fixed

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Screenshots or screen recordings

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Before	After
Image is displayed 2x the actual retina size	Image is displayed in its retina dimensions (50% smaller)

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