Wrap psd read in try and except

The purpose of this MR is to prevent the last 2 entries from being removed for every psd (when this is only required for buggy LALInference psds). Instead it only removes the last 2 entries if a ValueError is raised.

This is ready to be merged (subject to passing CI).

The CI is expected to fail because of bilby#489 (closed). However, if it passes everything else, this can be merged.

approved this merge request

merged

mentioned in commit f520d5f7