Channel state may duplicate messages when multiple messages with the same creation timestamp are present

[MartinCupela]

Description

If a refetch of the same message set takes place, it is possible, that the same message will be added to the channel state twice. This can happen when multiple messages have the same time of creation for example. The search algorithm finds a position of a message with different ID but the same creation timestamp. As the IDs do not match, the messages is added once again to the state next to the found message.