This fixes the following case:
<blockquote>
<span />Foobar
</blockquote>
Qt would see the end of <span>, and consider the current block
tag as closed, thus resetting the block format, thus losing the
margin set for the current block (due to blockquote).
If you do
<blockquote>
<span>Foo</span>Foobar
</blockquote>
instead, then the same would not happen, since hasBlock is set
to false when we append text to the current inline node.
[ChangeLog][QTextDocument] Add support for empty inline elements
in block tags.
Task-number: QTBUG-33336
Change-Id: Ic566edfec96cb8d44d1c02932bb195bc921d1580
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>