Fix preset.sh returning invalid http response

[mcarbonne]

Since a recent update of the firmware on my camera, I had a lot of error logs in my home assistant instance :

Failed to parse headers (url=http://XXXX/cgi-bin/preset.sh?action=go_preset&num=0): [MissingHeaderBodySeparatorDefect()], unparsed data: 'PTZ_CMD_GOTO_POS pPtzInfo->nXPos=1750 ,pPtzInfo->nYPos=1365\nContent-type: application/json\r\n\r\n'
Failed to parse headers (url=http://XXX/cgi-bin/preset.sh?action=go_preset&num=1): [MissingHeaderBodySeparatorDefect()], unparsed data: 'PTZ_CMD_GOTO_POS pPtzInfo->nXPos=1448 ,pPtzInfo->nYPos=159\nContent-type: application/json\r\n\r\n'

To reproduce the issue without home assistant :

$ curl -vvv -u "XXXX:XXXX" "http://XXXXX/cgi-bin/preset.sh?action=go_preset&num=0"
* Host XXXXXXX was resolved.
* IPv6: (none)
* IPv4: X.X.X.X
*   Trying X.X.X.X:X..
* Connected to XXXXX (X.X.X.X) port X
* Server auth using Basic with user 'admin'
> GET /cgi-bin/preset.sh?action=go_preset&num=0 HTTP/1.1
> Host: XXXXX
> Authorization: Basic xxxx
> User-Agent: curl/8.5.0
> Accept: */*
> 
< HTTP/1.1 200 OK
* Header without colon
* Closing connection
curl: (8) Header without colon

I found the culprit. For whatever reason, ptz binary do output something on stdout so I redirected the output to /dev/null.

[root@XXX]# ptz -f /mnt/mmc/sonoff-hack/etc/ptz_presets.conf -a go_preset -n 0
PTZ_CMD_GOTO_POS pPtzInfo->nXPos=1750 ,pPtzInfo->nYPos=1365

I also fixed a bash syntax error in the same file.
Maybe having shellcheck running in a github action would be a good idea, I can open another PR regarding this point (but this PR focuses on fixing the bug only)

[mcarbonne]

@roleoroleo the fix has been running for a few days without any issues on my setup.