https://msdn.microsoft.com/en-us/library/ms679351 describes that
"it is unsafe to take an arbitrary system error code returned from an API
and use FORMAT_MESSAGE_FROM_SYSTEM without FORMAT_MESSAGE_IGNORE_INSERTS"
Previously in case when an error string would contain inserts, function
returned error, so the error message wasn't shown (at least it didn't
crash, thanks to nullptr as the function's last argument).

As the function may fail, we now pre-nullify the buffer pointer to avoid
dereferencing uninitialized pointer later (though at least for some
Windows versions, the function nullifies the pointer in case of
FORMAT_MESSAGE_ALLOCATE_BUFFER, but there's no explicit guarantee of this).

Also release of allocated buffer is changed to recommended use of
HeapFree.

The code that doesn't make use of OUString is left directly calling
FormatMessage, to avoid introducing new dependencies. Where it makes
sense, we now use WindowsErrorString from <comphelper/windowserrorstring.hxx>

Change-Id: I834c08eb6d92987e7d3d01e2c36ec55e42aea848
Reviewed-on: https://gerrit.libreoffice.org/44206Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>