[gnome-usage/add-speedometer] speedometer: Don't add GtkLabel twice to Speedometer

[Felipe Borges <felipeborges src gnome org>]

commit ef3e0cb725850ab0235dadc3b89dd8efcf92ff0d
Author: Felipe Borges <felipeborges gnome org>
Date:   Tue Jan 8 15:07:08 2019 +0000

    speedometer: Don't add GtkLabel twice to Speedometer
    
    Fixes #56

 src/speedometer.vala | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/src/speedometer.vala b/src/speedometer.vala
index f307f5e..c7adc89 100644
--- a/src/speedometer.vala
+++ b/src/speedometer.vala
@@ -88,9 +88,12 @@ namespace Usage
         {
             /* This is a Vala bug. It will cause a "warning".
             (content_area as Buildable).add_child(builder, child, type);*/
-            if (child is Gtk.Label)
+            if (child is Gtk.Label) {
                 content_area.add(child as Gtk.Widget);
 
+                return;
+            }
+
             base.add_child(builder, child, type);
         }
     }