Use contextual date format to format datetime

When a datetime has min time, we must still use the contextual date format
instead of the OS.

issue9622
review326131002

tryton/common/domain_parser.py

@@ -338,14 +338,13 @@ def format_value(field, value, target=None, context=None):
     def format_datetime():
         if not value:
             return ''
-        format_ = (
-            date_format(context.get('date_format')) + ' ' + time_format(field))
         if not isinstance(value, datetime.datetime):
             time = datetime.datetime.combine(value, datetime.time.min)
         else:
             time = timezoned_date(value)
-        if time.time() == datetime.time.min:
-            format_ = '%x'
+        format_ = date_format(context.get('date_format'))
+        if time.time() != datetime.time.min:
+            format_ += ' ' + time_format(field)
         return time.strftime(format_)
 
     def format_date():