libsmack: fix label validation in smack_new_label_from_path
libsmack: fix label validation in smack_new_label_from_path

Off-by-one length was returned from the function. This patch fixes
the regression by doing full validation for the SMACK label.

Signed-off-by: Jarkko Sakkinen <6e0a3da6445cd298bc4a6b3aaa269075849c9510@linux.intel.com>

jobol/smack,jobol/smack,smack-team/smack,smack-team/smack