fix weather widget crash with no internet connection

weather-widget/weather.lua

@@ -62,9 +62,11 @@ local resp
 
 weather_timer:connect_signal("timeout", function ()
     local resp_json = http.request("http://api.openweathermap.org/data/2.5/weather?q=" .. city .."&appid=" .. open_map_key)
+    if (resp_json ~= nil) then
         resp = json.decode(resp_json)
         icon_widget.image = path_to_icons .. icon_map[resp.weather[1].icon]
         temp_widget:set_text(to_celcius(resp.main.temp))
+    end
 end)
 weather_timer:emit_signal("timeout")