libs/sys: fix checking for empty table

diff --git a/libs/sys/luasrc/sys.lua b/libs/sys/luasrc/sys.lua
index d6062482c6e9c5935b86de9174a2188e58b0ecd5..ad80ae5ba3fa4af47989b2df18f398651691aec2 100644 (file)
--- a/libs/sys/luasrc/sys.lua
+++ b/libs/sys/luasrc/sys.lua
@@ -701,7 +701,7 @@ function wifi.channels(iface)
                fd:close()
        end
 
-       if #cns == 0 then
+       if not ((pairs(cns))(cns)) then
                cns = {
                        2.412, 2.417, 2.422, 2.427, 2.432, 2.437,
                        2.442, 2.447, 2.452, 2.457, 2.462