Merge branch 'mh/notes-cleanup'

Code clean-up. * mh/notes-cleanup: load_subtree(): check that `prefix_len` is in the expected range load_subtree(): declare some variables to be `size_t` hex_to_bytes(): simpler replacement for `get_oid_hex_segment()` get_oid_hex_segment(): don't pad the rest of `oid` load_subtree(): combine some common code get_oid_hex_segment(): return 0 on success load_subtree(): only consider blobs to be potential notes load_subtree(): check earlier whether an internal node is a tree entry load_subtree(): separate logic for internal vs. terminal entries load_subtree(): fix incorrect comment load_subtree(): reduce the scope of some local variables load_subtree(): remove unnecessary conditional notes: make GET_NIBBLE macro more robust