- fix crash, if obj file contains degenerated faces

- added unittest for this case

closes #2382

git-svn-id: http://www.openmesh.org/svnrepo/OpenMesh/trunk@1236 fdac6126-5c0c-442c-9429-916003d36597

src/Unittests/TestFiles/cube-minimal-degenerated.obj

@@ -0,0 +1,29 @@
+g cube
+v  0.0  0.0  0.0
+v  0.0  0.0  1.0
+v  0.0  1.0  0.0
+v  0.0  1.0  1.0
+v  1.0  0.0  0.0
+v  1.0  0.0  1.0
+v  1.0  1.0  0.0
+v  1.0  1.0  1.0
+vn  0.0  0.0  1.0
+vn  0.0  0.0 -1.0
+vn  0.0  1.0  0.0
+vn  0.0 -1.0  0.0
+vn  1.0  0.0  0.0
+vn -1.0  0.0  0.0
+f  1//2  7//2  5//2
+f  1//2  3//2  7//2 
+f  1//6  4//6  3//6 
+f  1//6  2//6  4//6 
+f  3//3  8//3  7//3 
+f  3//3  4//3  8//3 
+f  5//5  7//5  8//5 
+f  5//5  8//5  6//5 
+f  1//4  5//4  6//4 
+f  1//4  6//4  2//4 
+f  2//1  6//1  8//1  8//1 2//1
+f  2//1  8//1  4//1 
+f  2//1  2//1  2//1 
+f  2//1  8//1  2//1