[][openwrt][common][ksmbd][fix crash due to null pointer]

[Description]
Fix crash due to trying to free a null pointer.

[Release-log]
N/A

Change-Id: I3a9e476f7db969f79c2df7c79a3782a2ded2e44c
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/7012801
1 file changed