Bug in rare case of trying to modify but pass empty dict

[merretbuurman]

This is a bug that can occur when we try to modify a handle record (via REST client), but pass an empty dict of changes.

In that case, pyhandle will try to return a variable that is not assigned, here:

https://github.com/EUDAT-B2HANDLE/PYHANDLE/blob/master/pyhandle/client/resthandleclient.py#L602

When the variable nothingchanges is True, the variable resp never gets defined or assigned, so we run into an exception here:

https://github.com/EUDAT-B2HANDLE/PYHANDLE/blob/master/pyhandle/client/resthandleclient.py#L578

pidify_1  |     self.__handle_client.modify_handle_value(handle, **record_kv)
pidify_1  |   File "/usr/local/lib/python3.12/site-packages/pyhandle/client/resthandleclient.py", line 490, in modify_handle_value
pidify_1  |     return self.__handle_modification(handle, ttl, add_if_not_exist, overwrite, **kvpairs)
pidify_1  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pidify_1  |   File "/usr/local/lib/python3.12/site-packages/pyhandle/client/resthandleclient.py", line 602, in __handle_modification
pidify_1  |     return json.loads(decoded_response(resp))['handle']
pidify_1  |                                        ^^^^
pidify_1  | UnboundLocalError: cannot access local variable 'resp' where it is not associated with a value