Allow rtp::Packet::*RawExtension to take 0 as an extension id

webrtc/modules/rtp_rtcp/source/rtp_packet.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 261 matching lines @@
   WriteAt(0, (data()[0] & 0xF0) | csrcs.size());
   size_t offset = kFixedHeaderSize;
   for (uint32_t csrc : csrcs) {
     ByteWriter<uint32_t>::WriteBigEndian(WriteAt(offset), csrc);
     offset += 4;
   }
   buffer_.SetSize(payload_offset_);
 }
 
 bool Packet::HasRawExtension(int id) const {
+  if (id == ExtensionManager::kInvalidId)
+    return false;
   RTC_DCHECK_GE(id, kMinExtensionId);
   RTC_DCHECK_LE(id, kMaxExtensionId);
   return extension_entries_[id - 1].offset != 0;
 }
 
 rtc::ArrayView<const uint8_t> Packet::GetRawExtension(int id) const {
+  if (id == ExtensionManager::kInvalidId)
+    return nullptr;
   RTC_DCHECK_GE(id, kMinExtensionId);
   RTC_DCHECK_LE(id, kMaxExtensionId);
   const ExtensionInfo& extension = extension_entries_[id - 1];
   if (extension.offset == 0)
     return nullptr;
   return rtc::MakeArrayView(data() + extension.offset, extension.length);
 }
 
 bool Packet::SetRawExtension(int id, rtc::ArrayView<const uint8_t> data) {
   auto buffer = AllocateRawExtension(id, data.size());
   if (buffer.empty())
     return false;
   RTC_DCHECK_EQ(buffer.size(), data.size());
   memcpy(buffer.data(), data.data(), data.size());
   return true;
 }
 
 rtc::ArrayView<uint8_t> Packet::AllocateRawExtension(int id, size_t length) {
+  if (id == ExtensionManager::kInvalidId)
+    return nullptr;
   RTC_DCHECK_GE(id, kMinExtensionId);
   RTC_DCHECK_LE(id, kMaxExtensionId);
   RTC_DCHECK_GE(length, 1);
   RTC_DCHECK_LE(length, 16);
 
   ExtensionInfo* extension_entry = &extension_entries_[id - 1];
   if (extension_entry->offset != 0) {
     // Extension already reserved. Check if same length is used.
     if (extension_entry->length == length)
       return rtc::MakeArrayView(WriteAt(extension_entry->offset), length);
@@ skipping 245 matching lines @@
 uint8_t* Packet::WriteAt(size_t offset) {
   return buffer_.data() + offset;
 }
 
 void Packet::WriteAt(size_t offset, uint8_t byte) {
   buffer_.data()[offset] = byte;
 }
 
 }  // namespace rtp
 }  // namespace webrtc