fix(img): ensure scroll has been initialized

Author: adamdbradley

src/components/content/content.ts

@@ -777,7 +777,7 @@ export class Content extends Ion implements OnDestroy, OnInit {
    * @private
    */
   imgsUpdate() {
-    if (this._imgs.length && this.isImgsUpdatable()) {
+    if (this._scroll.initialized && this._imgs.length && this.isImgsUpdatable()) {
       updateImgs(this._imgs, this.scrollTop, this.scrollHeight, this.directionY, IMG_REQUESTABLE_BUFFER, IMG_RENDERABLE_BUFFER);
     }
   }

src/components/tabs/test/basic/app-module.ts

@@ -187,7 +187,7 @@ export class Tab2 {
         <button ion-button (click)="appNavPop()">App Nav Pop</button>
       </p>
 
-      <ion-list [virtualScroll]="items" [headerFn]="headerFn">
+      <ion-list [virtualScroll]="items">
 
         <ion-item *virtualItem="let item">
           Item: {{item}}

src/components/virtual-scroll/test/cards/main.html

@@ -8,15 +8,15 @@
 
   <div [virtualScroll]="items" approxItemHeight="320px">
 
-    <ion-card *virtualItem="let item">
+    <ion-card *virtualItem="let item; let itemBounds = bounds;">
 
       <div>
-        <ion-img [src]="item.imgSrc" [height]="item.imgHeight" [alt]="item.name"></ion-img>
+        <ion-img [src]="item.imgSrc" [height]="item.imgHeight" [alt]="item.name" [bounds]="itemBounds"></ion-img>
       </div>
 
       <ion-item>
         <ion-avatar item-left>
-          <ion-img [src]="item.avatarSrc" height="40" width="40"></ion-img>
+          <ion-img [src]="item.avatarSrc" height="40" width="40" [bounds]="itemBounds"></ion-img>
         </ion-avatar>
         <h2>{{ item.name }}</h2>
       </ion-item>

src/util/scroll-view.ts

@@ -11,6 +11,7 @@ export class ScrollView {
   scrollStart = new Subject<ScrollEvent>();
   scroll = new Subject<ScrollEvent>();
   scrollEnd = new Subject<ScrollEvent>();
+  initialized: boolean;
 
   private _el: HTMLElement;
   private _js: boolean;
@@ -28,7 +29,9 @@ export class ScrollView {
   constructor(private _dom: DomController) {}
 
   init(ele: HTMLElement, contentTop: number, contentBottom: number) {
-    if (!this._el) {
+    if (!this.initialized) {
+      this.initialized = true;
+
       assert(ele, 'scroll-view, element can not be null');
       this._el = ele;