sync back inline input value if initial data is undefined

Author: yyx990803

src/directive.js

@@ -127,7 +127,8 @@ DirProto.update = function (value, init) {
             this._update(
                 this.filters
                     ? this.applyFilters(value)
-                    : value
+                    : value,
+                init
             )
         }
     }

src/directives/model.js

@@ -118,8 +118,12 @@ module.exports = {
         )
     },
 
-    update: function (value) {
+    update: function (value, init) {
         /* jshint eqeqeq: false */
+        // sync back inline value if initial data is undefined
+        if (init && value === undefined) {
+            return this._set()
+        }
         if (this.lock) return
         var el = this.el
         if (el.tagName === 'SELECT') { // select dropdown