Symptom:
Send messages unsuccessfully but without error alert when other side lost network and sign out/re-sign in.

Conditions:
Step to Reproduce:
1.A & B send/receive messages
2.A lost network
3.B keep sending messages ,meanwhile A is still 'Available'
4.A sign out when no network and in 'Not connect  to IM server'
5.A re-sign in after network recover
6.Check A&B messages 

Expect Result:
If the message send unsuccessfully ,B should receive error messages to reminder 

Actual Result:
No error messages