Panning the chart can stuck at the margins.

If the user is not careful at the margin of the chart, than panning the chart can stuck for a short time.
Panning the chart over the margin of the chart results that the user has to pan as much to the opposite direction in order the chart starts moving.

Steps To Reproduce
1. Open a c3js chart ( like here http://c3js.org/samples/interaction_zoom.html , zoom in a lite bit in order to make it pan able)
2. Pan to the left margin of the chart.
3. Try to pan the chart to the left forward. The chart-image will not move but you do it anyway.
4. Now pan to the right.

The chart-image will start moving only after several panning move, not immediately.