misc: pass NULL instead of 0 for pointer in variadic functions

misc: pass NULL instead of 0 for pointer in variadic functions

0 is not NULL (at least not in all cases), passing 0 into a variadic
function in a place where the consumer reads it as pointer might
leave parts of the pointer uninitilized and hence filled with random
data.

It seems that this used to work with gcc, but clang seems to treat the
0 in those places as a 32bit integer.

Type: fix

Signed-off-by: Ivan Shvedunov <ivan4th@gmail.com>
Signed-off-by: Andreas Schultz <andreas.schultz@travelping.com>
Change-Id: I37d975eef5a1ad98fbfb65ebe47d73458aafea00