Fixed small bug when supplying bytes variable to MachO() object

[ayylemao]

If supplying only bytes buffer to MachO() object and running parse(), self.file_name was not properly initialized leading to:

 macho = MachO(data=binary_bytes)
 macho.parse()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "machofile.py", line 391, in parse
    self.general_info = self.get_general_info()
  File "machofile.py", line 425, in get_general_info
    if self.file_path is None:
AttributeError: 'MachO' object has no attribute 'file_path'

fixed that bug by initializing file_path as None in case of only bytes supplied in constructor