fix(autocomplete): error when closing from a destroyed view

Fixes an error that was being thrown, because the autocomplete tries to run change detection on a destroyed view.

Fixes angular#7315.

src/lib/autocomplete/autocomplete-trigger.ts

@@ -117,6 +117,7 @@ export class MdAutocompleteTrigger implements ControlValueAccessor, OnDestroy {
   private _overlayRef: OverlayRef | null;
   private _portal: TemplatePortal<any>;
   private _panelOpen: boolean = false;
+  private _componentDestroyed = false;
 
   /** Strategy that is used to position the panel. */
   private _positionStrategy: ConnectedPositionStrategy;
@@ -156,6 +157,7 @@ export class MdAutocompleteTrigger implements ControlValueAccessor, OnDestroy {
               @Optional() @Inject(DOCUMENT) private _document: any) {}
 
   ngOnDestroy() {
+    this._componentDestroyed = true;
     this._destroyPanel();
   }
 
@@ -179,7 +181,9 @@ export class MdAutocompleteTrigger implements ControlValueAccessor, OnDestroy {
 
     this._resetPlaceholder();
 
-    if (this._panelOpen) {
+    // Note that in some cases this can end up being called after the component is destroyed.
+    // Add a check to ensure that we don't try to run change detection on a destroyed view.
+    if (this._panelOpen && !this._componentDestroyed) {
       this._panelOpen = false;
 
       // We need to trigger change detection manually, because