Add one line to fix an edge case in Safari

Situation:
When body tag has 'user-select:none', paste with Ctrl+V doesn't work in Safari

See [this CodePen for demo](http://codepen.io/getshao/pen/fwmuy)

Notice how copy and paste with Ctrl + C / Ctrl + V works in all browsers except Safari
Targeted fix to Safari only.
Changelog entry.
Merge branch 't/12506'