clang-modernize -use-nullptr

and s/\bNULL\b/nullptr/g for *.cpp/h/mm files not compiled on my machine

Source/Core/AudioCommon/XAudio2_7Stream.cpp

@@ -159,7 +159,7 @@ XAudio2_7::XAudio2_7(CMixer *mixer)
 	: SoundStream(mixer)
 	, m_mastering_voice(nullptr)
 	, m_volume(1.0f)
-	, m_cleanup_com(SUCCEEDED(CoInitializeEx(NULL, COINIT_MULTITHREADED)))
+	, m_cleanup_com(SUCCEEDED(CoInitializeEx(nullptr, COINIT_MULTITHREADED)))
 {
 }