[balsa] address-book: LibBalsaAddressBook is abstract

[Peter Bloomfield <peterb src gnome org>]

commit 5489a9e86a6887003b6cab98e0a5ed06dc8ec8ad
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Fri May 22 12:53:17 2020 -0400

    address-book: LibBalsaAddressBook is abstract
    
    Define it as such, to show that it cannot be instantiated. Similarly
    LibBalsaAddressBookText.

 libbalsa/address-book-text.c | 2 +-
 libbalsa/address-book.c      | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/libbalsa/address-book-text.c b/libbalsa/address-book-text.c
index 955b1a8b9..424503c58 100644
--- a/libbalsa/address-book-text.c
+++ b/libbalsa/address-book-text.c
@@ -82,7 +82,7 @@ typedef struct {
     LibBalsaCompletion *name_complete;
 } LibBalsaAddressBookTextPrivate;
 
-G_DEFINE_TYPE_WITH_PRIVATE(LibBalsaAddressBookText, libbalsa_address_book_text,
+G_DEFINE_ABSTRACT_TYPE_WITH_PRIVATE(LibBalsaAddressBookText, libbalsa_address_book_text,
         LIBBALSA_TYPE_ADDRESS_BOOK)
 
 typedef struct {
diff --git a/libbalsa/address-book.c b/libbalsa/address-book.c
index 9fd89666a..ab2cff316 100644
--- a/libbalsa/address-book.c
+++ b/libbalsa/address-book.c
@@ -51,7 +51,7 @@ static void libbalsa_address_book_real_load_config(LibBalsaAddressBook *
                                                   ab,
                                                   const gchar * group);
 
-G_DEFINE_TYPE_WITH_PRIVATE(LibBalsaAddressBook, libbalsa_address_book, G_TYPE_OBJECT)
+G_DEFINE_ABSTRACT_TYPE_WITH_PRIVATE(LibBalsaAddressBook, libbalsa_address_book, G_TYPE_OBJECT)
 
 static void
 libbalsa_address_book_class_init(LibBalsaAddressBookClass * klass)