fix(patch.js): Added a check for duplicated keys before addVnodes in patchVnodes function.

Added a check for duplicated keys in the case that addVnodes is called instead of createChildren or
updateChildren. This cover the case when a empty div is change into a div with a list of childrens
with a duplicated key inside after initial rendering (see issue vuejs#8832).

fix vuejs#8832

Author: DanielSanRocha

src/core/vdom/patch.js

@@ -543,6 +543,9 @@ export function createPatchFunction (backend) {
       if (isDef(oldCh) && isDef(ch)) {
         if (oldCh !== ch) updateChildren(elm, oldCh, ch, insertedVnodeQueue, removeOnly)
       } else if (isDef(ch)) {
+        if (process.env.NODE_ENV !== 'production') {
+          checkDuplicateKeys(ch)
+        }
         if (isDef(oldVnode.text)) nodeOps.setTextContent(elm, '')
         addVnodes(elm, null, ch, 0, ch.length - 1, insertedVnodeQueue)
       } else if (isDef(oldCh)) {