Make get_neighbor const

QTProject/triangle.cpp

@@ -192,7 +192,7 @@ void ibToTriangles(QVector<Vertex> *vb, QVector<unsigned int> &ib, QVector<Trian
     }
 }
 
-Triangle::Neighbor Triangle::Neighbors::get_neighbor(Triangle::Edge::Name name) {
+Triangle::Neighbor Triangle::Neighbors::get_neighbor(Triangle::Edge::Name name) const {
     switch (name) {
         case Triangle::Edge::Name::uv:
             return this->uv;

QTProject/triangle.h

@@ -31,7 +31,7 @@ class Triangle {
             Neighbor vw;
             Neighbor wu;
 
-            Triangle::Neighbor get_neighbor(Triangle::Edge::Name name);
+            Triangle::Neighbor get_neighbor(Triangle::Edge::Name name) const;
         };
 
         Triangle();