[FIX] orm: always save boolean function fields, even when they are false

Fixes #4292: searching for records when a related boolean field is `False`
always returns nothing.

openerp/osv/orm.py

@@ -2883,7 +2883,7 @@ class BaseModel(object):
                 # if val is a many2one, just write the ID
                 if type(val) == tuple:
                     val = val[0]
-                if val is not False:
+                if f._type == 'boolean' or val is not False:
                     cr.execute(update_query, (ss[1](val), key))
 
     def _check_selection_field_value(self, cr, uid, field, value, context=None):