clang-modernize -use-nullptr

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

Source/Core/VideoBackends/Software/SWCommandProcessor.cpp

@@ -101,7 +101,7 @@ void Init()
 	interruptSet = false;
 	interruptWaiting = false;
 
-	g_pVideoData = 0;
+	g_pVideoData = nullptr;
 	g_bSkipCurrentFrame = false;
 }