contour: Skip the move

When jumping between segments, we always
need to skip index 0, since thats the move.

This fixes the tangent checks in the
rectangle tests.

gsk/gskcontour.c

@@ -512,7 +512,7 @@ gsk_standard_contour_get_tangent (const GskContour *contour,
   if (t == 0 && direction == GSK_PATH_START)
     {
       /* Look at the previous segment */
-      if (idx > 0)
+      if (idx > 1)
         {
           idx--;
           t = 1;
@@ -533,7 +533,7 @@ gsk_standard_contour_get_tangent (const GskContour *contour,
         }
       else if (self->flags & GSK_PATH_CLOSED)
         {
-          idx = 0;
+          idx = 1;
           t = 0;
         }
     }