newbytes is unable to handle a generator as a parameter

After only checking that the parameter is Iterable, newbytes then checks the parameters len(). https://github.com/PythonCharmers/python-future/blob/39a066ed8c29a0b3a32adac2ffd407119fe9ea6d/src/future/types/newbytes.py#L106

https://repl.it/IwSF/2

print(repr(bytes.newbytes(x for x in range(0))))

Traceback (most recent call last):
  File "main.py", line 4, in <module>
    print(repr(bytes.newbytes(x for x in range(0))))
  File "/home/runner/bytes.py", line 103, in __new__
    if len(args[0]) == 0:
TypeError: object of type 'generator' has no len()

Including a check for Sized as well avoids this.

if isinstance(args[0], Sized) and len(args[0]) == 0:

https://repl.it/IwSF/1