fix issue with percentiles chart navigation

[brenol]

OK, so this one is actually weird.

From the point of view of code, the current implementation is correct.

From the point of view of usability, though, it's incorrect.

As the first chart in ali is latencyChart, pressing L the first time does not change to the next chart, which is percentiles.
This problem does not happen with backwards button (H), and is easily fixed with changing start position to 0 (which is a fact).

I'm finishing a PR that will fix this problem.

[nakabonne]

resolved by #71