[libgda] gda-basic-form: fix segfault creating new DSN

[Daniel Espinosa Ortiz <despinosa src gnome org>]

commit afc407abccda86a5bbb9baa414bcff26d24a97cd
Author: Daniel Espinosa <esodan gmail com>
Date:   Mon Sep 10 11:01:10 2018 -0500

    gda-basic-form: fix segfault creating new DSN

 libgda-ui/gdaui-basic-form.c | 46 ++++++++++++++++++++++++++++++++------------
 1 file changed, 34 insertions(+), 12 deletions(-)
---
diff --git a/libgda-ui/gdaui-basic-form.c b/libgda-ui/gdaui-basic-form.c
index dc56ca489..596a8e4ec 100644
--- a/libgda-ui/gdaui-basic-form.c
+++ b/libgda-ui/gdaui-basic-form.c
@@ -144,8 +144,15 @@ typedef struct {
 static void
 size_group_free (SizeGroup *sg)
 {
-       g_object_unref (sg->size_group);
-       g_free (sg);
+       g_return_if_fail (sg != NULL);
+       if (sg->size_group != NULL) {
+               g_object_unref (sg->size_group);
+               sg->size_group = NULL;
+       }
+}
+static SizeGroup*
+size_group_new (void) {
+       return g_new0 (SizeGroup,1);
 }
 
 typedef struct
@@ -410,6 +417,7 @@ static void
 get_rid_of_set (GdaSet *paramlist, GdauiBasicForm *form)
 {
        g_return_if_fail (GDAUI_IS_BASIC_FORM (form));
+       g_return_if_fail (paramlist != NULL);
        GSList *list;
        GdauiBasicFormPrivate *priv = gdaui_basic_form_get_instance_private (form);
 
@@ -423,8 +431,10 @@ get_rid_of_set (GdaSet *paramlist, GdauiBasicForm *form)
        g_signal_handlers_disconnect_by_func (paramlist,
                                              G_CALLBACK (paramlist_holder_type_set_cb), form);
 
-       g_object_unref (priv->set);
-       priv->set = NULL;
+       if (priv->set) {
+               g_object_unref (priv->set);
+               priv->set = NULL;
+       }
 
        if (priv->set_info) {
                g_object_unref (priv->set_info);
@@ -553,14 +563,16 @@ gdaui_basic_form_dispose (GObject *object)
        GdauiBasicFormPrivate *priv = gdaui_basic_form_get_instance_private (form);
 
        /* paramlist */
-       if (priv->set)
+       if (priv->set) {
                get_rid_of_set (priv->set, form);
+               priv->set = NULL;
+       }
 
        destroy_entries (form);
 
        if (priv->size_groups) {
-               g_slist_foreach (priv->size_groups, (GFunc) size_group_free, NULL);
-               g_slist_free (priv->size_groups);
+               g_slist_free_full (priv->size_groups, (GDestroyNotify) size_group_free);
+               priv->size_groups = NULL;
        }
 
 
@@ -727,13 +739,22 @@ destroy_entries (GdauiBasicForm *form)
        if (priv->s_entries) {
                GSList *list;
                for (list = priv->s_entries; list; list = list->next) {
+                       if (list->data == NULL) continue;
                        SingleEntry *sentry = (SingleEntry *) list->data;
 
                        disconnect_single_entry_signals (sentry);
-
-                       g_object_unref ((GObject *) sentry->entry);
-                       g_object_unref ((GObject *) sentry->label);
-                       g_free (sentry->label_title);
+                       if (sentry->entry != NULL) {
+                               g_object_unref ((GObject *) sentry->entry);
+                               sentry->entry = NULL;
+                       }
+                       if (sentry->label) {
+                               g_object_unref ((GObject *) sentry->label);
+                               sentry->label = NULL;
+                       }
+                       if (sentry->label_title != NULL) {
+                               g_free (sentry->label_title);
+                               sentry->label_title = NULL;
+                       }
                        g_free (sentry);
                }
                g_slist_free (priv->s_entries);
@@ -2265,7 +2286,7 @@ gdaui_basic_form_add_to_size_group (GdauiBasicForm *form, GtkSizeGroup *size_gro
        GdauiBasicFormPrivate *priv = gdaui_basic_form_get_instance_private (form);
 
        SizeGroup *sg;
-       sg = g_new (SizeGroup, 1);
+       sg = size_group_new ();
        sg->size_group = g_object_ref (size_group);
        sg->part = part;
        priv->size_groups = g_slist_append (priv->size_groups, sg);
@@ -2308,6 +2329,7 @@ gdaui_basic_form_remove_from_size_group (GdauiBasicForm *form, GtkSizeGroup *siz
        
        SizeGroup *sg;
        for (list = priv->size_groups; list; list = list->next) {
+               if (list->data == NULL) continue;
                sg = (SizeGroup*) list->data;
                if (sg->size_group == size_group) {
                        priv->size_groups = g_slist_remove (priv->size_groups, sg);