Fixing bug in `DMCSimulationResults`.

Introduced bug to `DMCSimulationResults._parse_info_file` in commit
5a217dbb9edd07232156689cf3ffd6fc330c386a. Added a call to
`get_result_path_prefix`, which should have been made to
`get_result_indices`. This was causing and odd result for the
`final_result_index` attribute, and was breaking the parsing of result
files.