Menu don't respond when all devices are filtered

[pyrog]

http://live.glidernet.org/#c=47.50850,6.63969&z=6&y=0

When y=0 the backend return no datas and the frontend crash in cunimb.js#L842

Empty result (no OGN devices at that time): 👍 http://live.glidernet.org/lxml.php?a=0&z=1&y=4

<markers></markers>

Empty result (no OGN devices at that time): 👎 http://live.glidernet.org/lxml.php?a=0&z=1&y=0

Result with some ICAO receivers : 👍 http://live.glidernet.org/lxml.php?a=0&z=1&y=1

<markers>
<m a="48.599030,8.525970,_5e,89a12f5e,1934,13:25:30,15,20,181,-0.8,1,Musbach,0,89a12f5e"/>
<m a="52.783150,7.533330,_13,c31cb513,1492,13:25:32,13,347,309,-1.6,8,Veendam,0,c31cb513"/>
<m a="51.019619,8.033680,_39,df562339,1279,13:15:11,634,27,219,-2.6,7,Wenscht,0,df562339"/>
</markers>