Revert "simplified iterator/index arithmetics using static casts. re g…

…entryx#49"

This reverts commit 627a545.

src/libgeodecomp/storage/reorderingunstructuredgrid.h

@@ -247,7 +247,9 @@ class ReorderingUnstructuredGrid : public GridBase<typename DELEGATE_GRID::CellT
         }
 
 		for (RowLengthVec::iterator i = reorderedRowLengths.begin(); i != reorderedRowLengths.end(); ) {
-			RowLengthVec::iterator nextStop = static_cast<RowLengthVec::iterator>((std::min)(static_cast<RowLengthVec::size_type>(i) + SIGMA, reorderedRowLengths.end()));
+			std::size_t currentIndex = i - reorderedRowLengths.begin();
+			std::size_t nextIndex = (std::min)(currentIndex + SIGMA, reorderedRowLengths.size());
+			RowLengthVec::iterator nextStop = reorderedRowLengths.begin() + currentIndex;
 
 			std::stable_sort(i, nextStop, [](const IntPair& a, const IntPair& b) {
 				return a.second > b.second;