JPA connector attempts to compress a Binary value using GZIPInputStream (which can only read already-compressed data)

The problem started out with MODE-958, but the underlying cause was determined to be a bug inside the JPA connector. Because of the strangeness of the Binary interface (which exposes an InputStream), we're trying to read it with a GZIPInputStream (SimpleJpaRepository line 886). But GZIPInputStream only works when the content is already in GZIP format.