[balsa] Do not dereference NULL GError pointer

[Peter Bloomfield <peterb src gnome org>]

commit 0c025796b92708a3c4a51c3994da530380eba4ef
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Tue May 2 20:59:40 2017 -0400

    Do not dereference NULL GError pointer
    
        * libbalsa/mailbox_pop3.c (libbalsa_mailbox_pop3_check): check
        for err == NULL.

 ChangeLog               |    7 +++++++
 libbalsa/mailbox_pop3.c |    6 ++++--
 2 files changed, 11 insertions(+), 2 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 9e34384..052260f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2017-05-02  Peter Bloomfield  <pbloomfield bellsouth net>
+
+       Do not dereference NULL GError pointer
+
+       * libbalsa/mailbox_pop3.c (libbalsa_mailbox_pop3_check): check
+       for err == NULL.
+
 2017-05-01  Peter Bloomfield  <pbloomfield bellsouth net>
 
        Assistant improvements
diff --git a/libbalsa/mailbox_pop3.c b/libbalsa/mailbox_pop3.c
index 5e79319..2ef2225 100644
--- a/libbalsa/mailbox_pop3.c
+++ b/libbalsa/mailbox_pop3.c
@@ -683,8 +683,10 @@ libbalsa_mailbox_pop3_check(LibBalsaMailbox * mailbox)
                }
 
                if (!result) {
-                       libbalsa_information(LIBBALSA_INFORMATION_ERROR, _("POP3 error: %s"), err->message);
-                       g_error_free(err);
+                       libbalsa_information(LIBBALSA_INFORMATION_ERROR, _("POP3 error: %s"),
+                                             err != NULL ? err->message : "?");
+                       if (err != NULL)
+                            g_error_free(err);
                }
 
                /* done - clean up */