it did not work for hex encoded obj_id.

Also:

• tests/pathslicing: improve tests for the check() method validate we do have the expected error, namely 'not a gzip' and 'wrong hash id'.

• pathslicing: fix the 'not a gzip' error message in check() write the hex obj id in the error message instead of the repr of the bytes.

• tests/pathslicing: add a test for check() that ensure it does work we only had tests for non-valid checks.

• Fixes test_objstorage_pathslicing.py's test_check_not_gzip.

• Fixes test_objstorage_pathslicing.py's test_check_ok.