[FIX] const functions should be marked const

src/core/dataHandler/WDataSetFibers.cpp

@@ -468,12 +468,12 @@ WFiberIterator WFiberIterator::operator--( int )
     return t;
 }
 
-WFiberIterator WFiberIterator::operator+ ( size_t n )
+WFiberIterator WFiberIterator::operator+ ( size_t n ) const
 {
     return WFiberIterator( m_fibers, m_index + n );
 }
 
-WFiberIterator WFiberIterator::operator- ( size_t n )
+WFiberIterator WFiberIterator::operator- ( size_t n ) const
 {
     return WFiberIterator( m_fibers, m_index - n );
 }

src/core/dataHandler/WDataSetFibers.h

@@ -631,14 +631,14 @@ public:
      *
      * \return The iterator on the new place.
      */
-    WFiberIterator operator+ ( size_t n );
+    WFiberIterator operator+ ( size_t n ) const;
 
     /**
      * Minus operator. Decrements the iterator \param n times.
      *
      * \return The iterator on the new place.
      */
-    WFiberIterator operator- ( size_t n );
+    WFiberIterator operator- ( size_t n ) const;
 
     /**
      * Compare to another fiber iterator.