typing: add a couple of assertions to lrucachedict to help pytype Fixes the following warnings: line 1488, in pop: No attribute 'markempty' on None [attribute-error] In Optional[Union[Any, _lrucachenode, nothing]] line 1578, in popoldest: No attribute 'markempty' on None [attribute-error] In Optional[Union[Any, _lrucachenode, nothing]] Differential Revision: https://phab.mercurial-scm.org/D7674

util: rename a variable to avoid confusing pytype Fixes the following warning: line 1205, in f: No attribute 'append' on Dict[nothing, nothing] [attribute-error] In Union[Dict[nothing, nothing], list] Differential Revision: https://phab.mercurial-scm.org/D7673