Test if count is callable before using it

ModelStorage.count has been added in 6.2 but there are existing Model that has
field with this name.

Closes #12016

trytond/trytond/model/fields/many2one.py

@@ -259,7 +259,7 @@ class Many2One(Field):
         else:
             _, target_name = name.split('.', 1)
         target_domain = [(target_name,) + tuple(domain[1:])]
-        if Target.count() < _subquery_threshold:
+        if callable(Target.count) and Target.count() < _subquery_threshold:
             query = Target.search(target_domain, order=[], query=True)
             return column.in_(query)
         else:

trytond/trytond/model/fields/one2many.py

@@ -337,7 +337,8 @@ class One2Many(Field):
             origin_where = origin.like(Model.__name__ + ',%')
             origin = origin_field.sql_id(origin, Target)
 
-        use_in = Target.count() < _subquery_threshold
+        use_in = (
+            callable(Target.count) and Target.count() < _subquery_threshold)
         if '.' not in name:
             if value is None:
                 if use_in:

trytond/trytond/model/modelsql.py

@@ -1647,7 +1647,9 @@ class ModelSQL(ModelStorage):
         main_table, _ = tables[None]
         if count:
             table = convert_from(None, tables)
-            if (limit is not None and limit < cls.count()) or offset:
+            if (limit is not None
+                    and callable(cls.count)
+                    and limit < cls.count()) or offset:
                 select = table.select(
                     Literal(1), where=expression, limit=limit, offset=offset
                     ).select(Count(Literal('*')))
@@ -1878,7 +1880,7 @@ class ModelSQL(ModelStorage):
                     'You can not update fields: "%s", "%s"' %
                     (field.left, field.right))
 
-            if len(ids) < max(cls.count() / 4, 4):
+            if callable(cls.count) and len(ids) < max(cls.count() / 4, 4):
                 for id_ in ids:
                     cls._update_tree(id_, field_name,
                         field.left, field.right)