Fixes two bugs related to padding in the jitter buffer.

- Pad packets (empty) were often NACKed even though they were received.
- Padding only frames (empty) were didn't properly update the decoding state,
  and would therefore be NACKed even though they were received.

TEST=trybots

BUG=1150

Review URL: https://webrtc-codereview.appspot.com/929031

git-svn-id: http://webrtc.googlecode.com/svn/trunk@3183 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/video_coding/main/source/generic_decoder.cc

@@ -185,7 +185,8 @@ WebRtc_Word32 VCMGenericDecoder::Decode(const VCMEncodedFrame& frame,
         _callback->Pop(frame.TimeStamp());
     }
     // Update the key frame decoded variable so that we know whether or not we've decoded a key frame since reset.
-    _keyFrameDecoded = (frame.FrameType() == kVideoFrameKey || frame.FrameType() == kVideoFrameGolden);
+    _keyFrameDecoded = (_keyFrameDecoded ||
+        frame.FrameType() == kVideoFrameKey);
     return ret;
 }