【bug】迁徙图打开失败，原因是找不到layerInfo.xyField字段

review by zhaoq

Author: ChenGuanglin

src/openlayers/mapping/WebMap.js

@@ -1447,9 +1447,10 @@ export class WebMap extends ol.Observable {
                 colTitles[i] = Util.trim(colTitles[i]);
             }
         }
+        // 迁徙图xyField暂时用from中的
         let fileCode = layerInfo.projection,
-            xIdx = colTitles.indexOf(Util.trim(layerInfo.xyField.xField)),
-            yIdx = colTitles.indexOf(Util.trim(layerInfo.xyField.yField)),
+            xIdx = colTitles.indexOf(Util.trim((layerInfo.xyField && layerInfo.xyField.xField) || (layerInfo.from && layerInfo.from.xField))),
+            yIdx = colTitles.indexOf(Util.trim((layerInfo.xyField && layerInfo.xyField.yField) || (layerInfo.from && layerInfo.from.yField))),
             baseLayerEpsgCode = this.baseProjection,
             features = [];