Mi Band 8: Fix chunked encryption

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/xiaomi/XiaomiCharacteristic.java

@@ -244,12 +244,13 @@ public class XiaomiCharacteristic {
         }
 
         if (shouldWriteChunked(currentSending)) {
+            // Prepend encrypted index
+            currentSending = ByteBuffer.allocate(2 + currentSending.length).order(ByteOrder.LITTLE_ENDIAN)
+                    .putShort(encryptedIndex++)
+                    .put(currentSending)
+                    .array();
+
             LOG.debug("Sending next - chunked");
-            // FIXME this is not efficient - re-encrypt with the correct key for chunked (assumes
-            //  final encrypted size is the same - need to check)
-            if (isEncrypted) {
-                currentSending = authService.encrypt(payload, (short) 0);
-            }
 
             sendingChunked = true;