duplicated inifinite hits with slow network

[iam4x]

Describe the bug 🐛
When using the infinite hits widget on a slow network, clicking show more button may load duplicated hits.

To Reproduce 🔍
Steps to reproduce the behavior:

1. Go to https://community.algolia.com/instantsearch.js/v2/dev-novel/?selectedStory=InfiniteHits.default
2. Force your network settings to a slow network (example 3G)
3. Click on "Show more"
4. Scroll down to the hits
5. See the duplicated entries

Expected behavior 💭
Do not load/display duplicated hits.

Screenshots 🖥

Environment:
Slow network

[bobylito]

Render is called if there are new results and if the search is stalled. There are no checks in the implementation that prevents this new rendering: https://github.com/algolia/instantsearch.js/blob/develop/src/connectors/infinite-hits/connectInfiniteHits.js#L105-L133 (This is a working hypothesis for now, I will double check)