[Libreoffice] [REVIEW] Fix for fdo#37764

[Kohei Yoshida]

I'd like to cherry-pick 

http://cgit.freedesktop.org/libreoffice/calc/commit/?id=e89169562aa48ed38f3e4c91a9d79346c7602bf9

to the 3-4 branch in order to fix

https://bugs.freedesktop.org/show_bug.cgi?id=37764

The change is pretty simple.  The old code incorrectly cached empty
cells in remote documents as empty strings instead of empty cells, the
former is not consider blank by the ISBLANK function whereas the latter
is.

Review appreciated.

Kohei

-- 
Kohei Yoshida, LibreOffice hacker, Calc
<kyoshida at novell.com>