read_non_compressed_block is broken

[joziasdelrios]

Per RFC-1951, the non-compressed block has 16-bit lengths, instead of 8-bit.
Then read_non_compressed_block should consume 8-bit instead of 16-bit lengths,
Also, the read_next_byte function makes a wrong byte alignment, as offset calculation is wrong.

[joziasdelrios]

Considering an example ASCII text file of 4 bytes (octets) with contents "1234", its gunzip compressed blocks (per RFC-1952) is composed of the following byte sequence (hexadecimal):
01 04 00 FB FF 31 32 33 34 [CRC-32] 04 00 00 00
First byte 0x01 has BFINAL=1 and BTYPE=00b as expected for a single/last-block without compression. Higher 5 bits are skipped for byte alignment.

[joziasdelrios]

04 00 and FB FF means the uncompressed block length of 4 written with 16-bit, non-inverted and then bitwise inverted.