loader: require .json extension for JSON files

Trying to parse every file other than *.yml as JSON file isn't the best
idea. It wastes time on trying to parse non-template files. It produces
warnings like "json Loader Failed to load (...)template" for files that
were never meant to be templates. It's a bad pracice in general.

Check for file extension before using json.loads().

Fixes: 0d2d16c ("Native JSON Template Support")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

src/invoice2data/extract/loader.py

@@ -72,12 +72,14 @@ def read_templates(folder=None):
                     except YAMLError as error:
                         logger.warning("Failed to load %s template:\n%s", name, error)
                         continue
-                else:
+                elif name.endswith(".json"):
                     try:
                         tpl = json.loads(template_file.read())
                     except ValueError as error:
                         logger.warning("json Loader Failed to load %s template:\n%s", name, error)
                         continue
+                else:
+                    continue
             tpl["template_name"] = name
 
             # Test if all required fields are in template