Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_coding/neteq/test/RTPencode.cc

Index: webrtc/modules/audio_coding/neteq/test/RTPencode.cc
diff --git a/webrtc/modules/audio_coding/neteq/test/RTPencode.cc b/webrtc/modules/audio_coding/neteq/test/RTPencode.cc
index f390f5330bb26f576e0f70caddf4369e60f5d96e..5a09fcc5a4912fe879e9ae7529a83cb2504ba9e2 100644
--- a/webrtc/modules/audio_coding/neteq/test/RTPencode.cc
+++ b/webrtc/modules/audio_coding/neteq/test/RTPencode.cc
@@ -1828,7 +1828,7 @@ void stereoDeInterleave(int16_t* audioSamples, size_t numSamples) {
     return;
 
   tempVec = (int16_t*)malloc(sizeof(int16_t) * numSamples);
-  if (tempVec == NULL) {
+  if (tempVec == nullptr) {
     printf("Error allocating memory\n");
     exit(0);
   }