bkctld-check-incs: Protect jail_config_epoch

Test if `incs_policy_file` exists before using it. Fixes #43.

CHANGELOG.md

@@ -19,6 +19,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 * tests: clean jail configuration after each test
+* bkctld-check-incs: Protect `jail_config_epoch`
 
 ### Security
 

lib/bkctld-check-incs

@@ -20,10 +20,10 @@ for jail_name in $("${LIBDIR}/bkctld-list"); do
     # Today in ISO format
     today_iso=$(date +"%Y-%m-%d")
 
-    # get jail last configuration date
-    jail_config_epoch=$(date --date "$(stat -c %y ${incs_policy_file})" +"%s")
-
     if [ -n "${incs_policy_file}" ]; then
+        # get jail last configuration date
+        jail_config_epoch=$(date --date "$(stat -c %y ${incs_policy_file})" +"%s")
+
         # loop for each line in jail configuration
         for line in $(cat ${incs_policy_file}); do
             # inc date in ISO format