Fix coverity defects: CID 147551, 147552

CID 147551: Type:dereference null return value
CID 147552: Type:dereference null return value

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: cao.xuewen <cao.xuewen@zte.com.cn>
Closes #5279