plot-connections: set axis limits properly
When set_xlim(), set_ylim() were called repeatedly on the same axes after every plot, subsequent calls were ignored and only the first call determined the axis limits.
This could result in charts where some data wouldn't be visible at all, since it'd plotted beyond the smaller axis limit. To fix this, ensure the axes limits are set only once -- when all the data is already plotted.
before this fix:
with the fix:
sample data: sample.json