try-catch load()

[Maw-Fox]

Fixes

• Check for truncated images for convert() operations, as it stands the error that is uncaught when this runs does not inform the user which file produced the error, this does that as well as skips the file in question.

[Maw-Fox]

Contemplating closing this pull request as I'm creating a branch to both optimize performance and allow dataset migration and this is relevant to such.

Thoughts

• When --resize is True, --data_migration (default: True), data migration would create a clone of the relative path to the dataset path, and output %DATASET%_cropped adjacent to the dataset directory. This is to make sure this expensive operation is only run once.
• Currently the .load() operation substantially extends validation time (from ~1000f/s to ~100f/s), while being more extensive it feels like for already-prepared datasets the slowdown is not worth it, despite the lack of verbose debugging upon hitting truncated/corrupted files. Subsequently the addition of --extended_validation (default: False) would allow users to easily perform one-time extended validation.
• The conversion to 3-channel RGB would be moved into the --resize default migration, further speeding up operations on already-validated datasets.