Trigger editing-done on ComboBox changed only if a row is selected

The CellRendererTime uses also a ComboBoxEntry for editing but parsing it on
every change does not work because the parsing will expect a valid time format
otherwise the current text will be erased.
So to keep the original goal of changeset 3591350f0018 which is to trigger
"editing-done" when an option from the drop-down menu is selected, the callback
on "changed" must ensure there is an active row selected.

issue5746
review28601002

tryton/gui/window/view_form/view/list_gtk/widget.py

@@ -39,7 +39,12 @@ def send_keys(renderer, editable, position, treeview):
     editable.editing_done_id = editable.connect('editing_done',
             treeview.on_editing_done)
     if isinstance(editable, (gtk.ComboBoxEntry, gtk.ComboBox)):
-        editable.connect('changed', treeview.on_editing_done)
+        def changed(combobox):
+            # "changed" signal is also triggered by text editing
+            # so only trigger editing-done if a row is active
+            if combobox.get_active_iter():
+                treeview.on_editing_done(combobox)
+        editable.connect('changed', changed)
 
 
 def realized(func):