Cannot handle submodules with spaces

[cbuchart]

An exception is thrown when trying to access submodules which name includes an space:

For example, following log is in a repository with a submodule named "Engine SDK":

fatal: cannot change to './external/Engine': No such file or directory
Exception in thread Thread-1:
Traceback (most recent call last):
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.9/lib/python3.9/threading.py", line 973, in _bootstrap_inner
    self.run()
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.9/lib/python3.9/threading.py", line 910, in run
    self._target(*self._args, **self._kwargs)
  File "/Users/cbuchart/Library/Python/3.9/lib/python/site-packages/parallelforeachsubmodule/pfs.py", line 22, in worker
    PFSProcess(submodule, path, command, counter, output_filter, cmd_func, output_func).run()
  File "/Users/cbuchart/Library/Python/3.9/lib/python/site-packages/parallelforeachsubmodule/process.py", line 15, in __init__
    self.__active_branch = self.get_current_branch(self.__cwd)[:-1]
  File "/Users/cbuchart/Library/Python/3.9/lib/python/site-packages/parallelforeachsubmodule/process.py", line 24, in get_current_branch
    return sub.check_output(['git', '-C', path, 'rev-parse', '--abbrev-ref', 'HEAD']).decode('utf-8')
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.9/lib/python3.9/subprocess.py", line 424, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
  File "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.9/lib/python3.9/subprocess.py", line 528, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['git', '-C', './external/Engine', 'rev-parse', '--abbrev-ref', 'HEAD']' returned non-zero exit status 128.