update function dump_part, no more erros with file .img not exists

[josezanatta1961]

def dump_part(part):
sys.stdout.write("Processing %s partition" % part.partition_name)
sys.stdout.flush()

out_file = open('%s/%s.img' % (args.out, part.partition_name), 'wb')
h = hashlib.sha256()

if args.diff:
    old_img_path = '%s/%s.img' % (args.old, part.partition_name)
    # Verifica se o arquivo existe, se não existir, cria um arquivo vazio
    if not os.path.exists(old_img_path):
        open(old_img_path, 'wb').close()
    
    old_file = open(old_img_path, 'rb')
else:
    old_file = None

for op in part.operations:
    data = data_for_op(op,out_file,old_file)
    sys.stdout.write(".")
    sys.stdout.flush()

print("Done")