skip over hover when inverting mouse position leads to null

- this can happen when the cursor on the bg rect but off
  the map (on curly projection types).

Author: etpinard

src/plots/geo/geo.js

@@ -89,7 +89,7 @@ proto.plot = function(geoCalcData, fullLayout, promises) {
         var mouse = d3.mouse(this),
             lonlat = _this.projection.invert(mouse);
 
-        if(isNaN(lonlat[0]) || isNaN(lonlat[1])) return;
+        if(!lonlat || isNaN(lonlat[0]) || isNaN(lonlat[1])) return;
 
         var evt = {
             target: true,