[glib/wip/otte/interface-types: 440/448] Use G_TYPE_INVALID instead of 0

[Matthias Clasen <matthiasc src gnome org>]

commit 8cda2d922e9fe4864a7ac2790d70f5b7849c0125
Author: Matthias Clasen <mclasen redhat com>
Date:   Sun Jul 12 15:16:33 2020 -0400

    Use G_TYPE_INVALID instead of 0
    
    This makes things more self-explanatory.

 gobject/gtype.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)
---
diff --git a/gobject/gtype.c b/gobject/gtype.c
index c90cad2a8..8aa50ae59 100644
--- a/gobject/gtype.c
+++ b/gobject/gtype.c
@@ -1695,11 +1695,12 @@ g_type_interface_prerequisites (GType  interface_type,
  *
  * Returns the instantiable prerequisite of an interface type.
  *
- * If the interface type has no instantiable prerequisite, 0 is returned.
+ * If the interface type has no instantiable prerequisite,
+ * G_TYPE_INVALID is returned.
  *
  * Since: 2.64
  *
- * Returns: the instantiable prerequisite type or 0 if none
+ * Returns: the instantiable prerequisite type or G_TYPE_INVALID if none
  **/
 GType
 g_type_interface_instantiable_prerequisite (GType interface_type)
@@ -1712,7 +1713,7 @@ g_type_interface_instantiable_prerequisite (GType interface_type)
 
   iface = lookup_type_node_I (interface_type);
   if (iface == NULL)
-    return 0;
+    return G_TYPE_INVALID;
 
   G_READ_LOCK (&type_rw_lock);
 
@@ -1732,7 +1733,7 @@ g_type_interface_instantiable_prerequisite (GType interface_type)
   if (inode)
     return NODE_TYPE (inode);
   else
-    return 0;
+    return G_TYPE_INVALID;
 }
 
 static IFaceHolder*