Correct sorting of tei:biblStruct when multiple dates available (#712)

[HelenaSabel]

Test and Test2 pass, but actual fix is untested (however, due to the simplicity of the change, it might be unnecessary)

[sydb]

I compared the HTML Guidelines built with this branch vs dev, and found no significant changes (not even to BIB, which surprised me).

The other two <xsl:sort> commands in html/html_core.xsl and the other one <xsl:sort> command in latex/latex_core.xsl¹ use the (path/to/nodes)[1] method rather than the head(path/to/nodes) method. I would mildly prefer that they all 5 use one or the other. I don’t really much care which, to be honest. (I had to look up what head() does, but as far as I can tell, they do the exact same thing.)

note
¹ Which begs the question — why is sorting different in HTML vs LaTeX?

[sabineseifert]

It looks good to me and I remember we talked about that in a stylesheets meeting. But I still feel insecure concerning such stylesheets issues and should better not be relied upon.. 😬