fix: extension + file permissions

botlib/curl.py

@@ -184,7 +184,9 @@ class Curl:
             if not parts:
                 raise URLError('URL not valid: "{}"'.format(url_str))
 
-            ext = parts.path.split('.')[-1] or 'unknown'
+            ext = parts.path.split('.')[-1]
+            if not ext or len(ext) > 4:
+                ext = 'unknown'
             file_path = os.path.join(dest_dir, fname + '.' + ext)
             if override or not os.path.isfile(file_path):
                 url = parts.geturl()