fix(chat): disable unusable history pagination (#676)

When the initial REST page returns empty messages, hasOlderMessages
was still set to true (offset > 0), causing an infinite loop of empty
load-more requests. Guard with && chatMessages.isNotEmpty().

Co-authored-by: M57 <Hy4ri@users.noreply.github.com>

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatViewModel.kt

@@ -1403,7 +1403,7 @@ class ChatViewModel(
                         state.copy(
                             messages = chatMessages,
                             isLoading = false,
-                            hasOlderMessages = offset > 0,
+                            hasOlderMessages = offset > 0 && chatMessages.isNotEmpty(),
                             isLoadingOlder = false,
                         )
                     }