Fixed migration issues.

src/datasource-zabbix/query.controller.js

@@ -33,11 +33,12 @@ export class ZabbixQueryController extends QueryCtrl {
 
     this.init = function() {
 
-      this.target = migrations.migrate(this.target);
-
       this.templateSrv = templateSrv;
       var target = this.target;
 
+      // Migrate old targets
+      target = migrations.migrate(target);
+
       var scopeDefaults = {
         metric: {},
         oldTarget: _.cloneDeep(this.target)
@@ -69,11 +70,6 @@ export class ZabbixQueryController extends QueryCtrl {
           {name: "max", value: "max"}
         ];
 
-        // Set avg by default
-        if (!target.downsampleFunction) {
-          target.downsampleFunction = this.downsampleFunctionList[0];
-        }
-
         this.initFilters();
       }
       else if (target.mode === 1) {