Editor focus: Don't trigger when typing while the mouse is outside the editor.

Merges [30817] to the 4.1 branch.

props avryl.
fixes #20668.

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git-svn-id: http://core.svn.wordpress.org/branches/4.1@30808 1a063a9b-81f0-0310-95a4-ce76da25c4cd