Fix vsnprintf SIGSEGV passing "%s" with no va_list args to pool_debug. (RhBug:1064459)
Fix vsnprintf SIGSEGV passing "%s" with no va_list args to pool_debug. (RhBug:1064459)

With a help from pmachata@redhat.com.

Conan-Kudo/libhif,hughsie/libhif,Conan-Kudo/libhif,rpm-software-management/libhif,rpm-software-management/libhif,edynox/libdnf,cgwalters/libhif,Conan-Kudo/libhif,cgwalters/libhif,rpm-software-management/libdnf,Conan-Kudo/libhif,rpm-software-management/libhif,rpm-software-management/libdnf,hughsie/libhif,hughsie/libhif,rpm-software-management/libdnf,cgwalters/libhif,edynox/libdnf,cgwalters/libhif,edynox/libdnf,rpm-software-management/libhif,rpm-software-management/libdnf,hughsie/libhif,edynox/libdnf