[fractal] Fix crashes when redacting messages

[Daniel Garcia Moreno <danigm src gnome org>]

commit 4faeabc838dc5b3dc045ae30323bf3697b78714a
Author: Sonja Heinze <sonjaleaheinze gmail com>
Date:   Thu Feb 20 13:44:36 2020 +0100

    Fix crashes when redacting messages
    
    Before, when deleting a message, the corresponding widget was removed
    from the listbox (field listbox of List), but its corresponding element
    was not removed from the VecDeque (field list of List). That lead to having
    elements in list whose corresponding widgets were not realized, triggering
    a crash when trying to get the relative position of those elements.
    
    This commit fixes that bug.

 fractal-gtk/src/widgets/room_history.rs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)
---
diff --git a/fractal-gtk/src/widgets/room_history.rs b/fractal-gtk/src/widgets/room_history.rs
index cc27416b..12cbe094 100644
--- a/fractal-gtk/src/widgets/room_history.rs
+++ b/fractal-gtk/src/widgets/room_history.rs
@@ -28,6 +28,9 @@ use gtk;
 use gtk::prelude::*;
 
 struct List {
+    /* With the exception of temporary widgets, only modify the fields list and listbox
+    through the methods add_top(), add_bottom(), and remove_item() to maintain the
+    1-1 correspondence between them. */
     list: VecDeque<Element>,
     new_divider_index: Option<usize>,
     playing_videos: Vec<(Rc<VideoPlayerWidget>, SignalHandlerId)>,
@@ -66,6 +69,11 @@ impl List {
         self.list.push_front(element);
     }
 
+    fn remove_item(&mut self, index: usize, row: &gtk::ListBoxRow) {
+        self.list.remove(index);
+        self.listbox.remove(row);
+    }
+
     fn create_new_message_divider(rows: Rc<RefCell<Self>>) -> widgets::NewMessageDivider {
         let rows_weak = Rc::downgrade(&rows);
         let remove_divider = move || {
@@ -567,7 +575,7 @@ impl RoomHistory {
         let msg_widget = msg.widget.clone()?;
         let msg_sender = msg.sender.clone();
         msg.msg.redacted = true;
-        rows.listbox.remove(msg_widget.get_listbox_row());
+        rows.remove_item(i, msg_widget.get_listbox_row());
 
         // If the redacted message was a header message let's set
         // the header on the next non-redacted message instead.