If the constructor of Cursor is called with unexpected arguments (ie when calling a `find` wrongly), the `__init__` method does not run at all, but `__del__` is still called and will (of course) crash.

This leads to some noise in the logged error on top of the real TypeError:
```
>>> pymongo.cursor.Cursor(wrong=1)
Exception ignored in: <function Cursor.__del__ at 0x1048129d8>
Traceback (most recent call last):
  File "/Users/arthur/dev/.venvs/Users--arthur--dev--dragonstone/lib/python3.7/site-packages/pymongo/cursor.py", line 241, in __del__
    self.__die()
  File "/Users/arthur/dev/.venvs/Users--arthur--dev--dragonstone/lib/python3.7/site-packages/pymongo/cursor.py", line 298, in __die
    already_killed = self.__killed
AttributeError: 'Cursor' object has no attribute '_Cursor__killed'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: __init__() got an unexpected keyword argument 'wrong'
```