[Libreoffice] [REVIEW][3-5][3-5-0] Honor pre-selected filter type

[Kohei Yoshida]

Hi there,

I'd like to have the attached patch pushed to the 3-5 branch and
preferably to the 3-5-0 branch as well.

It fixes 

https://bugs.freedesktop.org/show_bug.cgi?id=45084

I haven't committed this yet to master, since I wanted to have someone
else's opinion first.  To the best of my knowledge this change makes
sense.  Why clear the type and filter just because one of the type
detections fail?

*But*, since this type detection code is incredibly complex, not to
mention for the HTML type, in particular, there are multiple type
detection services involved with some sort of special handling (html
disguided as xls by virtue of the extension is just one of those special
cases), it's possible that in some dark weird corners it may do some
totally unexpected, surprising things.  But I hope not.

Anyhow, review and sign-off appreciated if appropriate.  If not,
suggestions welcome.

Oh, BTW, I've already tested the case of opening an html file having a
xls extension.  It still works after my change.

Kohei

-- 
Kohei Yoshida, LibreOffice hacker, Calc