Fix NullPointerException when connected but no video frame decoded

This fixes a crash seen when connecting to a host from the Android
Chromoting client. The painting code got called before a video frame had
been decoded, and tried to dereference a null Bitmap.

NOTRY=true

Review URL: https://codereview.chromium.org/47873012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233025 0039d316-1c4b-4281-b951-d872f2087c98

remoting/android/java/src/org/chromium/chromoting/DesktopView.java

@@ -85,6 +85,11 @@ public class DesktopView extends SurfaceView implements DesktopViewInterface, Ru
         }
 
         Bitmap image = JniInterface.getVideoFrame();
+        if (image == null) {
+            // This can happen if the client is connected, but a complete video frame has not yet
+            // been decoded.
+            return;
+        }
 
         int width = image.getWidth();
         int height = image.getHeight();