Do not use union to access FIXED_STRING<4> as int

https://en.cppreference.com/w/cpp/language/union:
> It's undefined behavior to read from the member of the union that wasn't most recently written.

components/esm/cellref.cpp

@@ -66,7 +66,7 @@ void ESM::CellRef::loadData(ESMReader &esm, bool &isDeleted)
     while (!isLoaded && esm.hasMoreSubs())
     {
         esm.getSubName();
-        switch (esm.retSubName().intval)
+        switch (esm.retSubName().toInt())
         {
             case ESM::FourCC<'U','N','A','M'>::value:
                 esm.getHT(mReferenceBlocked);