Force visibility-change checking in EditorView's afterAttach method

When an `EditorView` becomes attached, if hardware acceleration is enabled, the call to `pollDOM` is a no-op because there's already a refresh pending. This can cause problems, because then the initial measurements don't happen and (for example) the lineHeight is left as null - it'll be set on the next rendering, but not before subscribers to `workspaceView.eachEditorView` are notified.

I just ran into this working on smashwilson/merge-conflicts#77.

I left the original `pollDOM` call in so that everything else that it does still happens if there's no refresh waiting. If the other stuff should *also* happen on that first render, a better solution might be to add a `force` parameter to `pollDOM`, instead? Let me know what you think.