clang-modernize -use-nullptr

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

Source/Core/VideoBackends/Software/SWRenderer.cpp

@@ -28,7 +28,7 @@ static std::string s_sScreenshotName;
 
 // Rasterfont isn't compatible with GLES
 // degasus: I think it does, but I can't test it
-RasterFont* s_pfont = NULL;
+RasterFont* s_pfont = nullptr;
 
 void SWRenderer::Init()
 {
@@ -44,7 +44,7 @@ void SWRenderer::Shutdown()
 	if (GLInterface->GetMode() == GLInterfaceMode::MODE_OPENGL)
 	{
 		delete s_pfont;
-		s_pfont = 0;
+		s_pfont = nullptr;
 	}
 }