Measure: wrong length and segments displayed when measure with a line

[liuar]

1. Set the measure type to Distance and Area
   
2. click to add two points
   
3. a line is added to be measured
   

Result: there are 2 segments appear, total length = 2 * segment length

Expected: only 1 segment appear, total length isn't doubled.

If measure on Bing maps, there will be an un-caughted exception.

[liuar]

[Analysis]

If the measure type is set to Area, a polygon will e created no matter how many point are added. For instance, if user adds two points Point(0,0) and Point(1,1) into the map, measure widget will create a polygon Polygon((0,0) (1,1) (0,0))) which is not a valid polygon at all.

In Measure.js, var cg = geom.getCentroid(), which used the polygon's area as a divisor in the implement. The cg.x and cg.y will be NaN and cause the exception in Bing map.

[Solution]

Check the geom's area before calcaulate the centroid. If the area equals to zero, that means that the geom is invalid, and we just ignore the followed opertionations.

[liuar]

Fixed at http://trac.osgeo.org/fusion/changeset/2095