[balsa] abook-completion: Guard against null string

[Peter Bloomfield <peterb src gnome org>]

commit 3c85a2a922346d12660b03ba880fdf0932ad1ccb
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Fri Jun 21 21:09:38 2019 -0400

    abook-completion: Guard against null string
    
    * libbalsa/abook-completion.c (completion_data_new):

 ChangeLog                   | 6 ++++++
 libbalsa/abook-completion.c | 6 ++++--
 2 files changed, 10 insertions(+), 2 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 6e4964036..76f6780fb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2019-06-21  Peter Bloomfield  <pbloomfield bellsouth net>
+
+       Guard against null string.
+
+       * libbalsa/abook-completion.c (completion_data_new):
+
 2019-06-21  Peter Bloomfield  <pbloomfield bellsouth net>
 
        Fix a thinko
diff --git a/libbalsa/abook-completion.c b/libbalsa/abook-completion.c
index 0efbd13ae..d70e1f13b 100644
--- a/libbalsa/abook-completion.c
+++ b/libbalsa/abook-completion.c
@@ -62,8 +62,10 @@ completion_data_new(InternetAddress * ia, const gchar * nick_name)
 #ifdef CASE_INSENSITIVE_NAME
     string_n = g_utf8_normalize(string->str, -1, G_NORMALIZE_ALL);
     g_string_free(string, TRUE);
-    ret->string = g_utf8_casefold(string_n, -1);
-    g_free(string_n);
+    if (string_n != NULL) {
+        ret->string = g_utf8_casefold(string_n, -1);
+        g_free(string_n);
+    }
 #else
     ret->string = g_string_free(string, FALSE);
 #endif