unbound: dnsbl_module: (test-mode) assume a query can pass if a blocklist file is empty

src/opnsense/service/templates/OPNsense/Unbound/core/dnsbl_module.py

@@ -562,6 +562,10 @@ def arg_parse_is_json_file(filename):
         json.load(open(filename))
     except FileNotFoundError:
         raise argparse.ArgumentTypeError("non existing file")
+    except json.JSONDecodeError:
+        # in cases where a file exists, but we're unable to decode it (e.g. the file is empty),
+        # we should assume the blocklist has no entries.
+        pass
     except:
         raise argparse.ArgumentTypeError("No blocklist available")