TraceSet is interpreted incorrectly if no data is specified

[Siebje]

To reproduce:

• Create an empty trace set with the header containing only
  Header.TRS_VERSION: 2
• Try to open the trace set

Expected:

• The trace set can be opened

Actual:
[ERROR] 13:59:31 FIPy base_request_handler.py:_handle_request_exception:43 | Traceback (most recent call last):
[...]
File "\trsfile\engine\trs.py", line 301, in get_traces
parameters = self.read_parameter_data()
File "\trsfile\engine\trs.py", line 323, in read_parameter_data
parameters['LEGACY_DATA'] = ByteArrayParameter(data)
File "\trsfile\traceparameter.py", line 23, in init
raise ValueError('The value for a TraceParameter cannot be empty')

[Siebje]

This seems to be caused by the fact that no TraceParameterDefinitionMap is present in the provided header. However, I would expect that in this case an empty definition map is created automatically if TRS_VERSION 2 is specified,