Fix Bug 1553512: blank paragraphs when pasting (#5649)
Fix Bug 1553512: blank paragraphs when pasting (#5649)

See https://bugzilla.mozilla.org/show_bug.cgi?id=1553512

If `p:empty { display: none; }` is defined in the CKEditor stylesheet,
then pasting multiple lines of text also inserts an empty `<p></p>`
before the pasted content.

The "Source" button must be clicked twice to re-render the editor and
display the extraneous paragraphs.

I do not entirely understand why this resolves the issue, but it does.
mozilla/kuma,Elchi3/kuma,mozilla/kuma,Elchi3/kuma,mozilla/kuma,a2sheppy/kuma,Elchi3/kuma,escattone/kuma,mozilla/kuma,Elchi3/kuma,escattone/kuma,escattone/kuma,a2sheppy/kuma,a2sheppy/kuma,a2sheppy/kuma,a2sheppy/kuma,Elchi3/kuma,mozilla/kuma