Fix functions for empty blobs
Fix functions for empty blobs

Expands fix from #175

xinghun92/rusqlite,jgallagher/rusqlite,xinghun92/rusqlite,mikelodder7/rusqlcipher,jgallagher/rusqlite,mikelodder7/rusqlcipher,gwenn/rusqlite,xinghun92/rusqlite,gwenn/rusqlite,mikelodder7/rusqlcipher,gwenn/rusqlite,jgallagher/rusqlite