Reset datas['form'] only for form view

tryton/wizard/main.py

@@ -121,7 +121,7 @@ class Wizard(object):
 
             if 'datas' in res:
                 datas['form'] = res['datas']
-            else:
+            elif res['type'] == 'form':
                 datas['form'] = {}
             if res['type'] == 'form':
                 if not dia: