The big NULL replacement party part 5.

Right. ' = NULL' would get a lot of these.

src/RageSurface_Load.cpp

@@ -12,7 +12,7 @@
 
 static RageSurface *TryOpenFile( RString sPath, bool bHeaderOnly, RString &error, RString format, bool &bKeepTrying )
 {
-	RageSurface *ret = NULL;
+	RageSurface *ret = nullptr;
 	RageSurfaceUtils::OpenResult result;
 	if( !format.CompareNoCase("png") )
 		result = RageSurface_Load_PNG( sPath, ret, bHeaderOnly, error );