Reorder priority for conflicting datasets

[cguo02]

Our team is running into an edge case where we have datasets that contain conflicting non-conforming dataset (NCD) and sigmf compliant data files. For example, we have filename.sigmf-meta, filename.cdif, and filename.sigmf-data, where the sigmf-meta has core:dataset set to filename.cdif. Currently, if we use fromfile to read in filename.sigmf-meta, it will pair the meta file with the sigmf-data file rather than the cdif. Given the SigMF spec, we would expect that if core:dataset is set, that means we have a NCD (even if a sigmf-data file with a matching filename exists), thus the file specified by core:dataset should be prioritized over the sigmf-data file.

From the spec:
The full filename of the Dataset file this Metadata file describes, used ONLY with Non-Conforming Datasets
If a Recording does not have this field, it MUST have a compliant SigMF Dataset (NOT a Non-Conforming Dataset) which MUST use the same base filename as the Metadata file and use the .sigmf-data extension

[Teque5]

Issue Makes sense to me - especially since it's called out in the spec. I added a related test. Thanks for the PR.