Saveload: Fix upstream chunk load state not be cleared before load

src/saveload/saveload.cpp

@@ -101,6 +101,7 @@ namespace upstream_sl {
 	void SlFixPointers();
 	void SlFixPointerChunkByID(uint32 id);
 	void SlSaveChunkChunkByID(uint32 id);
+	void SlResetLoadState();
 }
 
 /** What are we currently doing? */
@@ -3516,6 +3517,8 @@ static SaveOrLoadResult DoLoad(LoadFilter *reader, bool load_check)
 	_sl.reader = new ReadBuffer(_sl.lf);
 	_next_offs = 0;
 
+	upstream_sl::SlResetLoadState();
+
 	if (!load_check) {
 		ResetSaveloadData();
 

src/saveload/upstream/saveload.cpp

@@ -2128,6 +2128,12 @@ void SlSaveChunkChunkByID(uint32 id)
 	SlSaveChunk(*ch);
 }
 
+/** Reset state prior to a load */
+void SlResetLoadState()
+{
+	_next_offs = 0;
+}
+
 SaveLoadTable SaveLoadHandler::GetLoadDescription() const
 {
 	assert(this->load_description.has_value());