Relabel identifiers tool needs better error message when line does not contain 2 columns

[galaxyproject-sentryintegration]

Sentry Issue: GALAXY-MAIN-Z50

ValueError: dictionary update sequence element #4 has length 1; 2 is required
  File "galaxy/tools/__init__.py", line 1969, in handle_single_execution
    rval = self.execute(
  File "galaxy/tools/__init__.py", line 2066, in execute
    return self.tool_action.execute(
  File "galaxy/tools/actions/model_operations.py", line 89, in execute
    self._produce_outputs(
  File "galaxy/tools/actions/model_operations.py", line 120, in _produce_outputs
    tool.produce_outputs(
  File "galaxy/tools/__init__.py", line 3816, in produce_outputs
    new_labels_dict = dict(source_new_label)

Exception caught while attempting to execute tool with id '__RELABEL_FROM_FILE__':

[mvdbeek]

Fixed in #18634