clang-modernize -use-nullptr

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

Source/Core/DiscIO/FileBlob.cpp

@@ -19,7 +19,7 @@ PlainFileReader* PlainFileReader::Create(const char* filename)
 	if (f)
 		return new PlainFileReader(f.ReleaseHandle());
 	else
-		return NULL;
+		return nullptr;
 }
 
 bool PlainFileReader::Read(u64 offset, u64 nbytes, u8* out_ptr)