omit station-dump if no IBSS-interface is present

In case no interface of type IBSS is found, the array interfaces is empty, nevertheless the for-loop iterates once (with empty values) causing the system-call to iw to fail.
Check interfaces before the loop to avoid garbage-output from iw on the status-page if meshing on wifi is deactivated.

package/gluon-status-page/files/lib/gluon/status-page/www/cgi-bin/status

@@ -73,6 +73,7 @@ io.write("<h2>Neighbours</h2>")
 
 local interfaces = util.split(util.trim(util.exec("iw dev | egrep 'type IBSS|type mesh' -B 5 | grep Interface | cut -d' ' -f2")))
 
+if interfaces ~= {} then
   for _, ifname in ipairs(interfaces) do
     io.write("<h3>" .. escape_html(ifname) .. "</h3>")
     io.write("<pre>")
@@ -88,6 +89,7 @@ for _, ifname in ipairs(interfaces) do
 
     io.write("</pre>")
   end
+end
 
 local stat, fastd_status = pcall(
   function()