Remove p1 after inserting point next to it

Because this insertion requires dereferencing p1. If it has been removed from the list, dereferencing it would remove it from memory so that would be an invalid pointer reference.

Contributes to debugging issue CURA-3274.

src/utils/polygon.cpp

@@ -837,7 +837,6 @@ void PolygonRef::smooth_corner_simple(ListPolygon& poly, const Point p0, const P
             Point b;
             bool success = LinearAlg2D::getPointOnLineWithDist(a, p1, p2, shortcut_length, b);
             // v02 has to be longer than ab!
-            p1_it.remove();
             if (success)
             { // if not success then assume b is negligibly close to 2, but rounding errors caused a problem
 #ifdef ASSERT_INSANE_OUTPUT
@@ -845,6 +844,7 @@ void PolygonRef::smooth_corner_simple(ListPolygon& poly, const Point p0, const P
 #endif // #ifdef ASSERT_INSANE_OUTPUT
                 ListPolyIt::insertPointNonDuplicate(p1_it, p2_it, b);
             }
+            p1_it.remove();
         }
     }
 }