u32: prevent memcpy from NULL
u32: prevent memcpy from NULL

Found by Clang static analyzer.

Fixes: 6cdc32df831a273007af7d24a3f75cd06e0ae738
Signed-off-by: Peter Wu <4b8373d016f277527198385ba72fda0feb5da015@lekensteyn.nl>
Signed-off-by: Thomas Haller <16e26612e4159990a6b3691e92592e691ff74132@redhat.com>

dsahern/libnl,kolyshkin/libnl,congwang/libnl,tklauser/libnl,greearb/libnl-ct,houstar/libnl,dsahern/libnl,tklauser/libnl,tgraf/libnl,vyos/libnl3,tgraf/libnl,cfriedt/libnl,cyclops8456/libnl3,cfriedt/libnl,baloo/libnl,kolyshkin/libnl,thom311/libnl,HolyShitMan/libnl-1,tklauser/libnl,mshirley/libnl,tgraf/libnl,claudelee/libnl,thom311/libnl,HolyShitMan/libnl-1,tklauser/libnl,honsys/libnl,tgraf/libnl,congwang/libnl,UnicronNL/libnl3,honsys/libnl,cfriedt/libnl,houstar/libnl,cfriedt/libnl,houstar/libnl,claudelee/libnl,claudelee/libnl,baloo/libnl,dsahern/libnl,UnicronNL/libnl3,vyos/libnl3,cyclops8456/libnl3,vyos/libnl3,claudelee/libnl,houstar/libnl,dsahern/libnl,baloo/libnl,UnicronNL/libnl3,thom311/libnl,mshirley/libnl,baloo/libnl,kolyshkin/libnl,HolyShitMan/libnl-1,greearb/libnl-ct,vyos/libnl3,HolyShitMan/libnl-1,congwang/libnl,cyclops8456/libnl3,greearb/libnl-ct,UnicronNL/libnl3,mshirley/libnl,mshirley/libnl,kolyshkin/libnl,congwang/libnl,cyclops8456/libnl3,honsys/libnl,honsys/libnl