Convert mask from and to bytes while decreasing

[maaktweluit]

2019-11-14 15:55:32 ERROR    golem                               Service Error: Traceback (most recent call last):
  File "/Users/mwu-gol/.pyenv/versions/3.6.8/lib/python3.6/threading.py", line 916, in _bootstrap_inner
    self.run()
  File "/Users/mwu-gol/.pyenv/versions/3.6.8/lib/python3.6/threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "/Users/mwu-gol/src/golem-project/golem/.venv/lib/python3.6/site-packages/twisted/_threads/_threadworker.py", line 46, in work
    task()
  File "/Users/mwu-gol/src/golem-project/golem/.venv/lib/python3.6/site-packages/twisted/_threads/_team.py", line 190, in doWork
    task()
--- <exception caught here> ---
  File "/Users/mwu-gol/src/golem-project/golem/.venv/lib/python3.6/site-packages/twisted/python/threadpool.py", line 250, in inContext
    result = inContext.theWork()
  File "/Users/mwu-gol/src/golem-project/golem/.venv/lib/python3.6/site-packages/twisted/python/threadpool.py", line 266, in <lambda>
    inContext.theWork = lambda: context.call(ctx, func, *args, **kw)
  File "/Users/mwu-gol/src/golem-project/golem/.venv/lib/python3.6/site-packages/twisted/python/context.py", line 122, in callWithContext
    return self.currentContext().callWithContext(ctx, func, *args, **kw)
  File "/Users/mwu-gol/src/golem-project/golem/.venv/lib/python3.6/site-packages/twisted/python/context.py", line 85, in callWithContext
    return func(*args,**kw)
  File "/Users/mwu-gol/src/golem-project/golem/golem/client.py", line 1639, in _run
    num_bits=self._update_num_bits)
  File "/Users/mwu-gol/src/golem-project/golem/golem/task/requestedtaskmanager.py", line 596, in decrease_task_mask
    task.mask.decrease(num_bits)
builtins.AttributeError: 'bytes' object has no attribute 'decrease'

[codecov]

Codecov Report

Merging #4895 into b0.22 will decrease coverage by 0.01%.
The diff coverage is 20%.

@@            Coverage Diff            @@
##            b0.22   #4895      +/-   ##
=========================================
- Coverage   89.21%   89.2%   -0.02%     
=========================================
  Files         233     233              
  Lines       21390   21392       +2     
=========================================
- Hits        19084   19083       -1     
- Misses       2306    2309       +3