handle variable-name attributes in writer

Author: lukaspie

src/pynxtools/dataconverter/helpers.py

@@ -590,8 +590,10 @@ def get_regex():
     results = get_regex().search(entry)
     if results is None:
         return entry
+
     if entry[0] == "@":
-        return "@" + results.group(1)
+        name = results.group(1)
+        return name if name.startswith("@") else "@" + name
     return results.group(1)