Fix DataPack Overwrite Regression (#862)

Some tests passed with the implementation prior to this commit, but those were edge cases. Good older behavior is now fully restored

core/logic/CDataPack.cpp

@@ -219,12 +219,16 @@ bool CDataPack::RemoveItem(size_t pos)
 	{
 		pos = position;
 	}
-
 	if (pos >= elements.length())
 	{
 		return false;
 	}
 
+	if (pos < position) // we're deleting under us, step back
+	{
+		--position;
+	}
+
 	switch (elements[pos].type)
 	{
 		case CDataPackType::Raw:
@@ -241,6 +245,5 @@ bool CDataPack::RemoveItem(size_t pos)
 	}
 
 	elements.remove(pos);
-	--position;
 	return true;
 }