[gnome-builder] config: add missing type precondition

[Christian Hergert <chergert src gnome org>]

commit f4edc62c7b36e800a644582b3b29611f07b18797
Author: Christian Hergert <chergert redhat com>
Date:   Sat Apr 14 14:10:55 2018 -0700

    config: add missing type precondition

 src/libide/config/ide-configuration.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/src/libide/config/ide-configuration.c b/src/libide/config/ide-configuration.c
index 1f2039ba9..96465139b 100644
--- a/src/libide/config/ide-configuration.c
+++ b/src/libide/config/ide-configuration.c
@@ -954,6 +954,7 @@ ide_configuration_set_environment (IdeConfiguration *self,
   IdeConfigurationPrivate *priv = ide_configuration_get_instance_private (self);
 
   g_return_if_fail (IDE_IS_CONFIGURATION (self));
+  g_return_if_fail (!environment || IDE_IS_ENVIRONMENT (environment));
 
   if (priv->environment != environment)
     {