[!362] Feature/uggrid avoid warnings

Merge branch 'feature/uggrid-avoid-warnings' into 'master'

ref:core/dune-grid Avoid a few compiler warnings in UGGrid.

See merge request [!362]

  [!362]: gitlab.dune-project.org/core/dune-grid/merge_requests/362

dune/grid/uggrid/uggridentity.cc

@@ -91,7 +91,7 @@ template <int cc>
 typename GridImp::template Codim<cc>::Entity
 UGGridEntity<0,dim,GridImp>::subEntity ( int i ) const
 {
-  assert(i>=0 && i < subEntities(cc));
+  assert(i>=0 && i < int(subEntities(cc)));
 
   typename UG_NS<dim>::template Entity<cc>::T* subEntity;
 

dune/grid/uggrid/uggridleafiterator.hh

@@ -68,7 +68,7 @@ namespace Dune {
 
     /** \brief Constructor setting up an 'end' iterator
      */
-    UGGridLeafIterator()
+    UGGridLeafIterator() : grid_(nullptr)
     {
       entity_.impl().setToTarget(nullptr,nullptr);
     }

dune/grid/uggrid/uggridleveliterator.hh

@@ -35,7 +35,7 @@ namespace Dune {
     enum {codimension = codim};
 
     //! Constructor
-    explicit UGGridLevelIterator()
+    explicit UGGridLevelIterator() : gridImp_(nullptr)
     {
       entity_.impl().setToTarget(nullptr,nullptr);
     }