Read receipt for current room sent unintentionally after opening a notification for another room

I've been observing this problem for a long time, but only now took the time to report it.

I'm currently using the TestFlight build (0.8.7 / 20190524161608)

# Steps to reproduce

1. Have 2 rooms you are joined to (let's call them Room A and Room B). There needs to be at least one other person in those rooms who can send test messages.
2. Navigate to Room **A**
3. Background the app (press the Home button)
4. Have the person send a message to both rooms
5. Check your notifications. Open the notification for Room **B** (note: this is the **other** room, not the one that you left riot-ios on)
6. Notice how you've just unintentionally read the messages for Room **A** as well, even though you never got to see them

This has frequently caused me to not see people's messages.

Start by reproducing the two-room notification flow on the TestFlight version described, then trace how opening a notification for Room B handles read receipts for the previously active Room A. Done means messages in Room A remain unread until that room's messages are actually viewed.

Written by the indexing model from the issue text.