[ Upstream commit d6d478ae ]

aa_label_merge() can return NULL for memory allocations failures
make sure to handle and set the correct error in this case.
Reported-by: Peng Hao <peng.hao2@zte.com.cn>
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>