[vis] make line charts render properly at small sizes

[ascott]

chart and axis are distorted/broken if the slice container is too small.

[hawkett]

Additional note: the broken state is dependent on the screen resolution - e.g. on my laptop, they are broken as in OP, but if I connect a larger screen, they work fine - without needing refresh. In general screen resolution should not affect correct rendering, as I could build a dashboard that looks great to me, and then send it someone else who will be unable to view it.

tl;dr - if rendering is going to fail, it should do so reliably.

[yileic]

#2413