Render issue when interrupting render with another render

* **C3 version**: 0.7.3
* **D3 version**:
* **Browser**: Firefox 68.0
* **OS**: Fedora 30

Whenever data is being loaded and another load happens before the previous one finishes, there will be some render issues. This is most prevalent when unloading when loading new data

Example: The purple line in this image is before the update. Hovering over the line will not cause the tooltip to appear

Hovering over where it should be:

CodeSandbox where I've been able to reproduce it. Here the `data2` should end up at 400, but don't change: https://codesandbox.io/s/modest-thunder-xh7bx?fontsize=14

Start with the linked CodeSandbox and reproduce an update while data is loading, especially unloading while loading new data. Compare the interrupted render with the expected result: data2 should reach 400 and the existing purple line should respond to hover with a tooltip.

Written by the indexing model from the issue text.