Prevent depacketizer OOB reads on zero-length VP8 payload.

webrtc/modules/rtp_rtcp/source/rtp_format_vp8.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_format_vp8.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_format_vp8.cc b/webrtc/modules/rtp_rtcp/source/rtp_format_vp8.cc
index 5202754caf4d13850ce526d6da3c9e599c962ebb..1dc799968d0b74daa53d63612391cfd18cf6dc1e 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_format_vp8.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_format_vp8.cc
@@ -668,6 +668,10 @@ bool RtpDepacketizerVp8::Parse(ParsedPayload* parsed_payload,
                                const uint8_t* payload_data,
                                size_t payload_data_length) {
   assert(parsed_payload != NULL);
+  if (payload_data_length == 0) {
+    LOG(LS_ERROR) << "Empty payload.";
+    return false;
+  }
 
   // Parse mandatory first byte of payload descriptor.
   bool extension = (*payload_data & 0x80) ? true : false;               // X bit