Client sometimes sends 2 read receipts

[malteish]

While monitoring the use of handleSubmitMessage, I noticed that a message "Hi" from Alice to Bob usually results in 3 invokations of the endpoint:

1. payload
2. deliveryReceipt
3. readReceipt
   (This assumes both Alice and Bob use the same delivery service)

However, sometimes handleSubmitMessage is invoked 4 times. This is the case when Bob is connected, but viewing another conversation. When switching tabs to the conversation with Alice, handleSubmitMessage is called 2 times. It should only be called once.