Filler char is unnecessarily created between <brs> and perhaps in other cases

[Piotrek Koszuliński]

While working on #12621 I noticed that ​this line accepts cases in which we don't need a filler char.

One of them is: <p><br>^<br></p>, however, the comment says that it also creates the filler char in empty paragraph, what doesn't make sense at all, because empty blocks should be filled with the bogus <br> and then the filler char is not necessary any more.

The line (as well as comment and referred ticket in which this line has not been added) is so vague that it should be carefully checked.

The only scenario which it seems that it should accept is an empty inline element.