Have UserDict.__init__() implicitly check for updating w/ bool(kwargs) instead of len() (pythonGH-12139)

Semantically the same, but more idiomatic by checking against `kwargs` instead of `len(kwargs)`.

Author: 0bsearch

Lib/collections/__init__.py

@@ -1016,7 +1016,7 @@ def __init__(*args, **kwargs):
  self.data = {}
  if dict is not None:
  self.update(dict)
- if len(kwargs):
+ if kwargs:
  self.update(kwargs)
  def __len__(self): return len(self.data)
  def __getitem__(self, key):