clang-modernize -use-nullptr

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

Source/Core/VideoBackends/OGL/PostProcessing.cpp

@@ -51,7 +51,7 @@ void Init()
 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 0); // disable mipmaps
 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
-	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
+	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1, 1, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
 	glBindFramebuffer(GL_FRAMEBUFFER, s_fbo);
 	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, s_texture, 0);
 	FramebufferManager::SetFramebuffer(0);
@@ -108,7 +108,7 @@ void Update ( u32 width, u32 height )
 		// alloc texture for framebuffer
 		glActiveTexture(GL_TEXTURE0+9);
 		glBindTexture(GL_TEXTURE_2D, s_texture);
-		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
+		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
 	}
 }