[Libreoffice] [REVIEW] Fix for #fdo36719

[Kohei Yoshida]

Here is another bug fix I'd like to push to the -3-4 branch.

https://bugs.freedesktop.org/show_bug.cgi?id=36719

Opening a document with a pivot table that is linked to a invalid
database source crashes Calc in various places.  The attached patch
fixes this.

The changes are mostly simple things such as checking for NULL pointers
before dereferencing.

I'm attaching a patch instead of cherry-picking because the commit I
pushed to master has a wrong bug ID in the message.

Anyway, review & sign-off appreciated.

Kohei

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