Release v0.1.2 don't error on unknown service type

Fix an error when service.Type is not a field of service_types and the
code attempts to call a nil value.

Turns out that service.Type can be the string "?", probably because
connman has not identified the type yet.

connman_widget-0.1.2-1.rockspec

@@ -1,8 +1,8 @@
 package = "connman_widget"
-version = "0.1.1-1"
+version = "0.1.2-1"
 source = {
   url = "git://github.com/stefano-m/awesome-connman_widget",
-  tag = "v0.1.1"
+  tag = "v0.1.2"
 }
 description = {
   summary = "A Connman widget for the Awesome Window Manager",

connman_widget.lua

@@ -178,10 +178,12 @@ local function get_status_icon(mgr)
     return build_icon_path(icon_statuses.unspecified.idle)
   elseif mgr.current_service then
     local service = mgr.current_service
-    return service_types[service.Type](service)
-  else
-    return build_icon_path(icon_statuses.unspecified.err)
+    local f = service_types[service.Type]
+    if type(f) == "function" then
+      return f(service)
+    end
   end
+  return build_icon_path(icon_statuses.unspecified.err)
 end
 
 local widget = wibox.widget.imagebox()