don't add empty line strings to line coordinates

Author: etpinard

src/lib/geojson_utils.js

@@ -38,7 +38,9 @@ exports.calcTraceToLineCoords = function(calcTrace) {
         }
     }
 
-    coords.push(lineString);
+    if(lineString.length > 0) {
+        coords.push(lineString);
+    }
 
     return coords;
 };