Custom keyboard shortcut doesn't work in Preview

I used "Run Shell Script" in Automator to make a custom keyboard shortcut to toggle WiFi on/off:

⌃⌥⌘W

I set it to:

Workflow receives no input in any application

and used the script:

if [[ `networksetup -getairportpower en0` == *On ]]
then
  networksetup -setairportpower en0 off
else
  networksetup -setairportpower en0 on
fi

This works in apps such as Firefox, but does nothing in Preview.

How can I make it work in Preview?

Thanks.