Fix empty channel slot handling

lib/providers/connection_provider.dart

@@ -848,10 +848,21 @@ class ConnectionProvider with ChangeNotifier {
       return true;
     } catch (e) {
       debugPrint('❌ [Provider] Failed to check slot $channelIdx: $e');
+      if (_isEmptyChannelQueryError(e)) {
+        debugPrint(
+          '   ℹ️  Treating slot $channelIdx as empty because the device reported it was not found',
+        );
+        return true;
+      }
       return false;
     }
   }
 
+  bool _isEmptyChannelQueryError(Object error) {
+    final message = error.toString().toLowerCase();
+    return message.contains('not found');
+  }
+
   Future<int?> findNextEmptyChannelSlot() async {
     if (!_activeService.isConnected) {
       throw Exception('Not connected to device');