【fix】unit空值

Author: songyumeng

src/common/util/MapCalculateUtil.js

@@ -22,8 +22,12 @@ import { Unit } from '../REST';
  * ```
  */
 export var getMeterPerMapUnit = function(mapUnit) {
-    var earchRadiusInMeters = 6378137;
     var meterPerMapUnit;
+    if(!mapUnit){
+      return meterPerMapUnit;
+    }
+    var earchRadiusInMeters = 6378137;
+    
     if (['m','meter','meters'].indexOf(mapUnit.toLocaleLowerCase())>-1) {
         meterPerMapUnit = 1;
     } else if (['degrees','deg','degree','dd'].indexOf(mapUnit.toLocaleLowerCase())>-1) {