Avoid comparison of unsigned and signed int

dune/contact/assemblers/largedeformationcoupling.cc

@@ -838,7 +838,7 @@ void LargeDeformationCoupling<field_type, GridType0,GridType1>::setupIndexPatter
 
   const auto& indexSet0 = grid0_->leafIndexSet();
   const auto& indexSet1 = grid1_->leafIndexSet();
-  int size0{indexSet0.size(dim)},size1{indexSet1.size(dim)};
+  size_t size0(indexSet0.size(dim)),size1(indexSet1.size(dim));
 
   MatrixIndexSet nmIndices(nObstacles, size0);
   MatrixIndexSet mIndices(nObstacles, size1);