application: Check libhandy version at compilation

This only enables the dark style preference if we have
a libhandy version of 1.5.0 or newer.

src/calls-application.c

@@ -358,15 +358,19 @@ startup (GApplication *application)
 {
   g_autoptr (GtkCssProvider) provider = NULL;
   g_autoptr (GError) error = NULL;
+#if HDY_CHECK_VERSION(1, 5, 0)
   HdyStyleManager *style_manager;
+#endif
 
   G_APPLICATION_CLASS (calls_application_parent_class)->startup (application);
 
   hdy_init ();
 
+#if HDY_CHECK_VERSION(1, 5, 0)
   style_manager = hdy_style_manager_get_default ();
 
   hdy_style_manager_set_color_scheme (style_manager, HDY_COLOR_SCHEME_PREFER_LIGHT);
+#endif
 
   if (!call_audio_init (&error))
     {