[gthumb] Fixed crash when selecting other images after deleting

[Paolo Bacchilega <paobac src gnome org>]

commit da2a196b9d2d991fd649c9ed94071938da901b48
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Sun Sep 13 08:46:59 2020 +0200

    Fixed crash when selecting other images after deleting
    
    This only happened when selecting images with a range select
    (shift + mouse click) after deleting the last images in a list.
    
    The last_selected_pos value was not updated after deleting or adding
    files to the list.
    
    Closes #126

 gthumb/gth-grid-view.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)
---
diff --git a/gthumb/gth-grid-view.c b/gthumb/gth-grid-view.c
index 83fc300ae..1b2bdffe5 100644
--- a/gthumb/gth-grid-view.c
+++ b/gthumb/gth-grid-view.c
@@ -2187,6 +2187,13 @@ model_row_deleted_cb (GtkTreeModel *tree_model,
        else if (pos == self->priv->focused_item)
                self->priv->focused_item = -1;
 
+       /* update the last selected position */
+
+       if (pos < self->priv->last_selected_pos)
+               self->priv->last_selected_pos--;
+       else if (pos == self->priv->last_selected_pos)
+               self->priv->last_selected_pos = -1;
+
        /* relayout from the minimum changed position */
 
        _gth_grid_view_queue_relayout_from_position (self, pos);
@@ -2238,6 +2245,11 @@ model_row_inserted_cb (GtkTreeModel *tree_model,
        if (pos <= self->priv->focused_item)
                self->priv->focused_item++;
 
+       /* update the last selected position */
+
+       if (pos <= self->priv->last_selected_pos)
+               self->priv->last_selected_pos++;
+
        /* relayout from the minimum changed position */
 
        _gth_grid_view_queue_relayout_from_position (self, pos);
@@ -2666,7 +2678,7 @@ _gth_grid_view_select_range (GthGridView     *self,
        }
 
        for (scan = g_list_nth (self->priv->items, a);
-            a <= b;
+            (a <= b) && (scan != NULL);
             a++, scan = scan->next)
        {
                GthGridViewItem *item = scan->data;