refactor: replace NULL with nullptr across C++ codebase

Excludes vendored C libs (zlib, Miles, DirectXMath, boost, Iggy).

Minecraft.Client/Textures/MemTexture.cpp

@@ -17,7 +17,7 @@ MemTexture::MemTexture(const std::wstring& _url, std::uint8_t* pbData,
     // 4J - remember to add deletes in here for any created BufferedImages when
     // implemented
     loadedImage = new BufferedImage(pbData, dataBytes);
-    if (processor == NULL) {
+    if (processor == nullptr) {
     } else {
         // loadedImage=processor.process(ImageIO.read(huc.getInputStream()));
     }