Does not run with -B flag
Trying to use xmrminer in background, it can't start. it reports:

`Non-existent CUDA device #1 specified in --cuda-devices option`

Without `-B` I can start it fine.

This is the invocation:

`/usr/src/xmrig-nvidia/build/xmrig-nvidia -u [addr] -o de.minexmr.com:7777 -k --cuda-devices=1 -B -l /var/log/xmrig.log`

Using:

```
# /usr/src/xmrig-nvidia/build/xmrig-nvidia -V
XMRig 2.5.2
 built on Mar 28 2018 with GCC 7.3.1
 features: x86_64 AES-NI

libuv/1.19.2
libmicrohttpd/0.9.59
CUDA/9.10

GeForce GTX 1060 6GB @ 1771/4004 MHz 32x30 0x0 arch:61 SMX:10

linux 4.15.12-1-ARCH
```