fix(transition): fix out-in transition getting stuck with v-if (#7023)

fix #6687

Author: neelance

src/platforms/web/runtime/components/transition.js

@@ -161,7 +161,9 @@ export default {
       oldChild &&
       oldChild.data &&
       !isSameChild(child, oldChild) &&
-      !isAsyncPlaceholder(oldChild)
+      !isAsyncPlaceholder(oldChild) &&
+      // #6687 component root is a comment node
+      !(oldChild.componentInstance && oldChild.componentInstance._vnode.isComment)
     ) {
       // replace old child transition data with fresh one
       // important for dynamic transitions!