FIX: Preserve Post Voting mobile layout when the first post is not loaded

When visiting a post under a post-voting topic, and the first post is not loaded, say, /t/topic/2/10, the style of the plugin failed to load, causing the voting button to overlap with the post text in mobile view.

This commit change the connector to topic-above-posts instead of topic-above-posts-stream, so that the style is loaded normally.

Also added some spec to avoid regression.