[gegl] graph: clear child nodes when setting node operation

[Ell <ell src gnome org>]

commit 3ff1e27c41c691e76fd831e3c6f9ef192f379cc7
Author: Ell <ell_se yahoo com>
Date:   Tue Jun 2 22:48:39 2020 +0300

    graph: clear child nodes when setting node operation
    
    When setting a GeglNode's operation object, clear any child nodes,
    to allow for replacing a node's op from a meta-op to a non-meta-op.

 gegl/graph/gegl-node.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gegl/graph/gegl-node.c b/gegl/graph/gegl-node.c
index 9054be160..de4fa23be 100644
--- a/gegl/graph/gegl-node.c
+++ b/gegl/graph/gegl-node.c
@@ -1426,6 +1426,8 @@ gegl_node_set_operation_object (GeglNode      *self,
   while (self->pads)
     gegl_node_remove_pad (self, self->pads->data);
 
+  gegl_node_remove_children (self);
+
   gegl_operation_attach (operation, self);
 
   /* FIXME: This should handle all input pads instead of just these 3 */