Fix crashes inside libgnome-keyring.

They happen because we are passing literal 0 (which is interpreted as
int) to varargs function, which expects it to be a pointer. The result
may be a garbage within libgnome-keyring, because int may be 32 bits
and pointers 64 bits wide.
Merge pull request #14 from krnowak/libgnome-keyring-crash-fix

Fix crashes inside libgnome-keyring.