UI: fix display of disk size and IOPS fields in the scale VM form (apache#11553)

Author: bernardodemarco

ui/src/views/compute/ScaleVM.vue

@@ -232,8 +232,8 @@ export default {
         getAPI('listDiskOfferings', {
           id: this.selectedOffering.diskofferingid
         }).then(response => {
-          const diskOfferings = response.listdiskofferingsresponse.diskoffering || []
-          if (this.diskOfferings) {
+          const diskOfferings = response?.listdiskofferingsresponse?.diskoffering || []
+          if (diskOfferings?.length > 0) {
             this.selectedDiskOffering = diskOfferings[0]
           }
         }).catch(error => {