Back Navigation in ThreadUI not working

[FelberMartin]

Describe the bug

When the user is in the ThreadUI screen and presses the Android back button (not the BackArrow in the top left), the user stays in the Thread screen. After pressing the back button a second time, the user is navigated back to the conversation overview, skipping the ChatList screen.

To Reproduce
Steps to reproduce the behavior:

1. Go to any Chat
2. Click on a post to open the thread screen
3. Press the Android back button -> nothing happens
4. Press the back button again -> the ConversationOverview is shown

Expected behavior
Pressing the back button once should show the ChatList screen.