UI: Fix irrelevant conversion options in import instance modal (#8838)

Author: vishesh92

ui/src/views/tools/ImportUnmanagedInstance.vue

@@ -713,7 +713,7 @@ export default {
         page: 1
       })
       this.fetchKvmHostsForConversion()
-      if (this.resource.disk.length > 1) {
+      if (this.resource?.disk?.length > 1) {
         this.updateSelectedRootDisk()
       }
     },

ui/src/views/tools/ManageInstances.vue

@@ -1074,6 +1074,7 @@ export default {
       this.sourceHypervisor = value
       this.sourceActions = this.AllSourceActions.filter(x => x.sourceDestHypervisors[value])
       this.form.sourceAction = this.sourceActions[0].name || ''
+      this.selectedVmwareVcenter = undefined
       this.onSelectSourceAction(this.form.sourceAction)
     },
     onSelectSourceAction (value) {