EEschema polylines aren't closed.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/18262

eeschema/sch_shape.cpp

@@ -578,7 +578,10 @@ void SCH_SHAPE::AddPoint( const VECTOR2I& aPosition )
     if( GetShape() == SHAPE_T::POLY )
     {
         if( m_poly.IsEmpty() )
+        {
             m_poly.NewOutline();
+            m_poly.Outline( 0 ).SetClosed( false );
+        }
 
         m_poly.Outline( 0 ).Append( aPosition, true );
     }

eeschema/tools/ee_point_editor.cpp

@@ -1272,7 +1272,19 @@ int EE_POINT_EDITOR::removeCorner( const TOOL_EVENT& aEvent )
 
     commit.Modify( shape, m_frame->GetScreen() );
 
-    poly.Remove( getEditedPointIndex() );
+    int idx = getEditedPointIndex();
+    int last = (int) poly.GetPointCount() - 1;
+
+    if( idx == 0 && poly.GetPoint( 0 ) == poly.GetPoint( last ) )
+    {
+        poly.Remove( idx );
+        poly.SetPoint( last-1, poly.GetPoint( 0 ) );
+    }
+    else
+    {
+        poly.Remove( idx );
+    }
+
     setEditedPoint( nullptr );
 
     updateItem( shape, true );