Update print preview when a printer becomes available

We laizily request printer capabilities and when they are reported
we were not updating the preview and as a result the content was not
rendered, hence pages showing an empty state.

bug:17514117

Change-Id: Icfee7eaa1ab63f5e4d7655d4057ef2110c27cd43

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

@@ -1993,6 +1993,7 @@ public class PrintActivity extends Activity implements RemotePrintDocument.Updat
             if ((isActive && gotCapab) || (becameActive && hasCapab)) {
                 if (hasCapab && capabChanged) {
                     updatePrintAttributesFromCapabilities(newCapab);
+                    updatePrintPreviewController(false);
                 }
                 onPrinterAvailable(newPrinterState);
             } else if ((becameInactive && hasCapab) || (isActive && lostCapab)) {