Charts - Address issue in which column/bar graphs with missing data and groupMarkers set to true

Proposed fix for: https://github.com/yui/yui3/issues/1392

Need to test:
- [x] ie6
- [x] ie7
- [x] ie8
- [x] ie9
- [x] ie10
- [x] ie11
- [x] mac safari
- [x] ios safari
- [x] android 2.3.4
- [x] android 4.1.1
- [x] firefox
- [x] chrome