Fix ordering of library function call and include of library #68

Fix validation bool function and turn on halt and exit flag `set -e` to guard against regression.

pre_cache_action.sh

@@ -1,15 +1,17 @@
 #!/bin/bash
 
+set -e
+
+# Include library.
+script_dir="$(dirname -- "$(realpath -- "${0}")")"
+source "${script_dir}/lib.sh"
+
 # Debug mode for diagnosing issues.
 # Setup first before other operations.
 debug="${4}"
 validate_bool "${debug}" debug 1
 test ${debug} == "true" && set -x
 
-# Include library.
-script_dir="$(dirname -- "$(realpath -- "${0}")")"
-source "${script_dir}/lib.sh"
-
 # Directory that holds the cached packages.
 cache_dir="${1}"