Crash in print spooler when back pressed before content update complted.

We are updating the printed content asynchronously. If the user cancels
printing before the first update is complete the spooler components are
in a destroyed state but we attempt to handle the completed update resulting
in a crash. Now if printing is cancelled we ignore the update result.

bug:18525491

Change-Id: I1ef47a17de19896cba2c7a1dd2bfc205065e0a5a

packages/PrintSpooler/src/com/android/printspooler/model/PageContentRepository.java

@@ -486,7 +486,9 @@ public final class PageContentRepository {
                 protected Void doInBackground(Void... params) {
                     synchronized (mLock) {
                         try {
-                            mRenderer.closeDocument();
+                            if (mRenderer != null) {
+                                mRenderer.closeDocument();
+                            }
                         } catch (RemoteException re) {
                             /* ignore */
                         }

packages/PrintSpooler/src/com/android/printspooler/ui/PrintActivity.java

@@ -487,6 +487,10 @@ public class PrintActivity extends Activity implements RemotePrintDocument.Updat
                 requestCreatePdfFileOrFinish();
             } break;
 
+            case STATE_PRINT_CANCELED: {
+                updateOptionsUi();
+            } break;
+
             default: {
                 updatePrintPreviewController(document.changed);