comment
fix closures with multiple `lends` tags (#569)

There were three separate problems here:

1. The visitor called `trackVars` at the wrong time for `AssignmentExpression` and `VariableDeclarator` nodes, which prevented JSDoc from setting the `funcscope` property correctly.
2. The `funcscope` property was being added to `VariableDeclarator` nodes. It should only be added to `AssignmentExpression` nodes.
3. We were trying to resolve the variable name `____` in `AssignmentExpression` nodes. This is a special value we add to the source code so that the `lends` tag will work, and it should never be resolved against the enclosing scope.

The previous, buggy behavior looked reasonable in most cases, but it didn't work for closures that contain multiple `lends` tags.