Use gsl::at instead of subscript operator

src/buffer/out/AttrRow.cpp

@@ -522,7 +522,7 @@ void ATTR_ROW::ReplaceAttrs(const TextAttribute& toBeReplacedAttr, const TextAtt
     _list.resize(newRun.size());
     for (auto i = 0; i < _list.size(); i++)
     {
-        _list[i] = newRun[i];
+        _list.at(i) = newRun.at(i);
     }
 
     return S_OK;