Better handling for non-existing publisher ID
Better handling for non-existing publisher ID

A side note: I do not own a windows phone, so I wasn't able to test this commit.
johnwerd/wallpapers,Telerik-Verified-Plugins/AdMob,floatinghotpot/cordova-plugin-admob,floatinghotpot/cordova-plugin-admob,floatinghotpot/cordova-plugin-admob,johnwerd/wallpapers,floatinghotpot/cordova-plugin-admob,Telerik-Verified-Plugins/AdMob,johnwerd/wallpapers,Telerik-Verified-Plugins/AdMob,Telerik-Verified-Plugins/AdMob,johnwerd/wallpapers