docs(example): Avoid UnboundLocalError for get_object when exception

[100gle]

I used get_object as example shown:

# Get data of an object.
try:
    response = client.get_object("my-bucket", "my-object")
    # Read data from response.
finally:
    response.close()
    response.release_conn()

But I got the UnboundLocalError when encountered exception in get_object.

UnboundLocalError: local variable 'response' referenced before assignment

However, the fget_object api has handled this situation, so I think get_object should do so.

+response = None
try:
    response = client.get_object("my-bucket", "my-object")
    # Read data from response.
except Exception:
    # User can handle exception and don't worry about the `UnboundLocalError`.
finally:
+    if response:
        response.close()
        response.release_conn()