fix(router-view): add condition to see whether the tree is inactive

close vuejs#2552

Author: zrh122

Diff for: src/components/view.js

@@ -26,11 +26,14 @@ export default {
     let depth = 0
     let inactive = false
     while (parent && parent._routerRoot !== parent) {
-      if (parent.$vnode && parent.$vnode.data.routerView) {
-        depth++
-      }
-      if (parent._inactive) {
-        inactive = true
+      const vnodeData = parent.$vnode && parent.$vnode.data
+      if (vnodeData) {
+        if (vnodeData.routerView) {
+          depth++
+        }
+        if (vnodeData.keepAlive && parent._inactive) {
+          inactive = true
+        }
       }
       parent = parent.$parent
     }