Bug report

When pass an empty buffer to binascii.a2b_uu(), it reads a byte past the end of the empty buffer and returns the bytes object of the length encoded in that byte. For example:

>>> import binascii
>>> binascii.a2b_uu(memoryview(b'#86)C')[:0])
b'\x00\x00\x00'

When pass an empty bytes or bytearray object, it returns the bytes object of length 32, because they always have a null byte past the end.

>>> binascii.a2b_uu(b'')
b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'

In general, reading past the end of the buffer is an undefined behavior. It can cause segfault if the empty buffer refers to the end of mmaped memory.