Correcting a concurrent modification crash

app/build.gradle.kts

...main/java/de/kuschku/quasseldroid/ui/chat/ChatActivity.kt

.../quasseldroid/ui/chat/buffers/BufferViewConfigFragment.kt

...de/kuschku/quasseldroid/ui/chat/input/ChatlineFragment.kt

...chku/quasseldroid/ui/chat/messages/MessageListFragment.kt

...rc/main/java/de/kuschku/quasseldroid/util/AvatarHelper.kt

.../quasseldroid/util/compatibility/AndroidHandlerService.kt