Fix buffer underflow bug that crashes the app in Samsung S8 running Android 8

Author: martinmarinov

drivers/src/main/java/info/martinmarinov/drivers/usb/cxusb/CxUsbDvbDevice.java

@@ -174,7 +174,7 @@ private void dvb_usb_generic_rw(@NonNull byte[] wbuf, int wlen, @Nullable byte[]
 
             // put delay here if needed
 
-            if (rbuf != null) {
+            if (rbuf != null && rlen >= 0) {
                 actlen = usbDeviceConnection.bulkTransfer(controlEndpointIn, rbuf, rlen, 5_000);
                 if (actlen < rlen) {
                     if (actlen >= 0) actlen = -1;