[vala] codegen: Don't emit g_type_add_instance_private() in *_register_type()

[Rico Tzschichholz <ricotz src gnome org>]

commit cb669029dbd56e1d60586b39161f4948250c2f56
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Fri Jul 13 19:14:55 2018 +0200

    codegen: Don't emit g_type_add_instance_private() in *_register_type()
    
    This fixes warnings like "sys:1: Warning: cannot add private field to
    invalid (non-instantiatable) type ..."
    
    Regression of df56f916e52e5efe3876afed59a6190f6cead1c8

 codegen/valatyperegisterfunction.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/codegen/valatyperegisterfunction.vala b/codegen/valatyperegisterfunction.vala
index c1811d949..750537500 100644
--- a/codegen/valatyperegisterfunction.vala
+++ b/codegen/valatyperegisterfunction.vala
@@ -213,7 +213,7 @@ public abstract class Vala.TypeRegisterFunction {
                        type_init.add_statement (new CCodeExpressionStatement (add_class_private_call));
                }
 
-               if (cl != null && (cl.has_private_fields || cl.get_type_parameters ().size > 0)) {
+               if (!plugin && cl != null && (cl.has_private_fields || cl.get_type_parameters ().size > 0)) {
                        var ccall = new CCodeFunctionCall (new CCodeIdentifier 
("g_type_add_instance_private"));
                        ccall.add_argument (new CCodeIdentifier (type_id_name));
                        ccall.add_argument (new CCodeIdentifier ("sizeof (%sPrivate)".printf (get_ccode_name 
(cl))));