Fix #900

Allow HTML files with meta tags that don't have a "name" and "content"
field to be read by the HTMLReader.
For example, "<meta charset="utf-8" />" might appear in an HTML
document.  Without this change, this causes an exception.

It's simply the pull request #900 addapted with the #932 one.
I don't know if I did it right, but it works fine for me.