Validating a user's edits in a tree view

[Chris Seaton <chris chrisseaton com>]

I have a tree view that has editable cells. I validate what the user's 
edit (specifically, not letting them leave a cell empty) in the edited 
signal handler.

When the validation fails I want to start to edit the cell again. 
However, doing this inside the signal callback raises 
"(cspassword:8442): Gtk-CRITICAL **: file gtktreeviewcolumn.c: line 3229 
(_gtk_tree_view_column_start_editing): assertion 
`tree_column->editable_widget == NULL' failed"

What can I do? What do most people do for validating tree cells being 
edited?

Thanks.

Chris Seaton