fix crash when getting previousChatMessage

when adapter has no items adapter!!.items[1].item will crash with IndexOutOfBoundsException

This could happen e.g. when chat history is cleared.

error was:

Exception java.lang.IndexOutOfBoundsException: Index 1 out of bounds for length 0
  at jdk.internal.util.Preconditions.outOfBounds (Preconditions.java:64)
  at jdk.internal.util.Preconditions.outOfBoundsCheckIndex (Preconditions.java:70)
  at jdk.internal.util.Preconditions.checkIndex (Preconditions.java:266)
  at java.util.Objects.checkIndex (Objects.java:359)
  at java.util.ArrayList.get (ArrayList.java:434)
  at com.nextcloud.talk.chat.ChatActivity.processMessagesFromTheFuture (ChatActivity.kt:2666)
  at com.nextcloud.talk.chat.ChatActivity.access$processMessagesFromTheFuture (ChatActivity.kt:209)
  at com.nextcloud.talk.chat.ChatActivity$initObservers$12$1.invokeSuspend (ChatActivity.kt:875)
  at com.nextcloud.talk.chat.ChatActivity$initObservers$12$1.invoke (Unknown Source:8)
  at com.nextcloud.talk.chat.ChatActivity$initObservers$12$1.invoke (Unknown Source:4)
  at kotlinx.coroutines.flow.FlowKt__TransformKt$onEach$$inlined$unsafeTransform$1$2.emit (Emitters.kt:219)
  at kotlinx.coroutines.flow.FlowKt__ErrorsKt$catchImpl$2.emit (Errors.kt:154)
  at kotlinx.coroutines.flow.FlowKt__TransformKt$onEach$$inlined$unsafeTransform$1$2.emit (Emitters.kt:220)
  at kotlinx.coroutines.flow.SharedFlowImpl.collect$suspendImpl (SharedFlow.kt:392)
  at kotlinx.coroutines.flow.SharedFlowImpl$collect$1.invokeSuspend (Unknown Source:15)
  at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith (ContinuationImpl.kt:33)
  at kotlinx.coroutines.DispatchedTask.run (DispatchedTask.kt:104)
  at android.os.Handler.handleCallback (Handler.java:942)
  at android.os.Handler.dispatchMessage (Handler.java:99)
  at android.os.Looper.loopOnce (Looper.java:201)
  at android.os.Looper.loop (Looper.java:288)
  at android.app.ActivityThread.main (ActivityThread.java:7932)
  at java.lang.reflect.Method.invoke
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:548)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:942)

Signed-off-by: Marcel Hibbe <[email protected]>

app/src/main/java/com/nextcloud/talk/chat/ChatActivity.kt

@@ -2663,8 +2663,8 @@ class ChatActivity :
             chatMessage.activeUser = conversationUser
 
             adapter?.let {
-                val previousChatMessage = adapter!!.items[1].item
-                if (previousChatMessage is ChatMessage) {
+                val previousChatMessage = it.items?.getOrNull(1)?.item
+                if (previousChatMessage != null && previousChatMessage is ChatMessage) {
                     chatMessage.isGrouped = groupMessages(chatMessage, previousChatMessage)
                 }
                 chatMessage.isOneToOneConversation =