Raise an exception when attempting to decompressing empty data

[Rogdham]

From Zstandard specification:

Zstandard compressed data is made of one or more frames.

Currently, we allow to decompress empty data:

>>> decompress(b"")
b''

After the fix, this is not allowed anymore:

>>> decompress(b"")
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    decompress(b"")
    ~~~~~~~~~~^^^^^
pyzstd.ZstdError: Decompression failed: zstd data ends in an incomplete frame, maybe the input data was truncated. Decompressed data is 0 bytes.