fix keep-alive nested child components

src/core/vdom/patch.js

@@ -143,7 +143,7 @@ export function createPatchFunction (backend) {
       if (isDef(i = data.hook) && isDef(i = i.destroy)) i(vnode)
       for (i = 0; i < cbs.destroy.length; ++i) cbs.destroy[i](vnode)
     }
-    if (isDef(i = vnode.child)) {
+    if (isDef(i = vnode.child) && !data.keepAlive) {
       invokeDestroyHook(i._vnode)
     }
     if (isDef(i = vnode.children)) {