Invalid geo map country code causes drawing bug

[mjanulaitis]

The bug
When you specify an invalid country code for the geo map, the drawing function breaks from the loop rather than continuing to the next heatland.

To Reproduce
Steps to reproduce the behavior:

1. Create the GeoMap control and load is with valid and invalid countries.
2. Notice only the countries prior to the invalid country are drawn.

Expected behavior
The loop should continue to draw the next country.

The Fix
CoreHeatLandSeries line 134:

if (mapLand is null) return;

Should be

if (mapLand is null) continue;