[gnome-builder] completion: fix page up/down when not at boundaries

[Christian Hergert <chergert src gnome org>]

commit 81308a39eebd67f9e6901be86004a2581dbe21df
Author: Christian Hergert <chergert redhat com>
Date:   Thu Jun 14 13:25:02 2018 -0700

    completion: fix page up/down when not at boundaries

 src/libide/completion/ide-completion-list-box.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)
---
diff --git a/src/libide/completion/ide-completion-list-box.c b/src/libide/completion/ide-completion-list-box.c
index aa2e379ec..0559c342d 100644
--- a/src/libide/completion/ide-completion-list-box.c
+++ b/src/libide/completion/ide-completion-list-box.c
@@ -57,9 +57,11 @@ struct _IdeCompletionListBox
   guint n_rows;
 
   /*
-   * The currently selected index within the result set.
+   * The currently selected index within the result set. Signed to
+   * ensure our math in various places allows going negative to catch
+   * lower edge.
    */
-  guint selected;
+  gint selected;
 
   /*
    * This is set whenever we make a change that requires updating the
@@ -825,7 +827,7 @@ ide_completion_list_box_move_cursor (IdeCompletionListBox *self,
                                      GtkMovementStep       step,
                                      gint                  direction)
 {
-  guint n_items;
+  gint n_items;
   gint offset;
 
   g_return_if_fail (IDE_IS_COMPLETION_LIST_BOX (self));
@@ -836,6 +838,10 @@ ide_completion_list_box_move_cursor (IdeCompletionListBox *self,
   if (!(n_items = g_list_model_get_n_items (G_LIST_MODEL (self->context))))
     return;
 
+  /* n_items is signed so that we can do negative comparison */
+  if (n_items < 0)
+    return;
+
   if (step == GTK_MOVEMENT_BUFFER_ENDS)
     {
       if (direction > 0)
@@ -863,9 +869,9 @@ ide_completion_list_box_move_cursor (IdeCompletionListBox *self,
   if (step == GTK_MOVEMENT_PAGES)
     direction *= self->n_rows;
 
-  if (((gint)self->selected + direction) > n_items)
+  if ((self->selected + direction) > n_items)
     self->selected = n_items - 1;
-  else if (((gint)self->selected + direction) < 0)
+  else if ((self->selected + direction) < 0)
     self->selected = 0;
   else
     self->selected += direction;