This change lets the coinstatsindex fail loudly in case the internal muhash state differs from the last finalized output saved on disk, which would indicate that the muhash state somehow got out of sync. This should generally not happen since both are written to disk in a batch but core#24076 seems to indicate that the might still be an issue.
Note that the actual fix for the mentionned issue is not in this backport. It is in core#24138.
This is a backport of core#24133