pass a copy when opening dialog

otherwise, any changes the dialog makes will reflect in the calling
view's object

dashboard/src/components/DockerRegistryDialog.vue

@@ -66,6 +66,7 @@ async function onSubmit() {
 
 defineExpose({
   async open(r = null) {
+    r = r ? JSON.parse(JSON.stringify(r)) : null; // make a copy
     busy.value = false;
     formError.value = {};
     registry.value = r;