Bug 895007. Handle zero size native drawing more gracefully. r=mattwoodrow

This fixes null drawtarget crashes

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extra : rebase_source : e7edd25c21edc636fad1a88940d97db4af269f0b
Bug 895078. Implement ScaledFontMac::CopyGlyphsToBuilder. r=mattwoodrow

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extra : rebase_source : e18c584de856676b84c9aac50021f255185a677a