Fix some wrong usage of ATTRIBUTE_NONNULL()

Fix some wrong usage of ATTRIBUTE_NONNULL()

The virStateInitialize() function has ATTRIBUTE_NONNULL()
referring to @root argument (incorrectly anyway) but in
daemonRunStateInit() NULL is passed in anyway.

Then there is virCommandAddArgPair() which also has
ATTRIBUTE_NONNULL() for one of its arguments and then checks the
argument for being NULL anyways.

Signed-off-by:Bihong Yu <yubihong@huawei.com>
Reviewed-by:Chuan Zheng <zhengchuan@huawei.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>