lossless gzip not finalizing wile FITS object is open

[esheldon]

This hidden test case fails:

fitsio/fitsio/tests/test_image_compression.py

Line 101 in 6f9590a

def _test_compressed_write_read_fitsobj(compress):

But this one, where the fits object is closed works

fitsio/fitsio/tests/test_image_compression.py

Line 30 in 6f9590a

def test_compressed_write_read(compress):

Note after writes fits_flush_file is called so this might be an issue in cfitsio