PythonEnvsReducer.resolveEnv() should fall back to wrapped locator.

[ericsnowcurrently]

Current PythonEnvsReducer.resolveEnv() returns undefined if the requested environment is not one provided by iterEnvs(). That means the wrapped locator never gets a chance to resolve the environment. Instead PythonEnvsReducer.resolveEnv() should fall back to the wrapped locator in that situation.

[ericsnowcurrently]

@int19h