fix crash when removing non-last columns

Fixes: https://github.com/damus-io/notedeck/issues/445

src/app.rs

@@ -729,8 +729,10 @@ fn render_damus_mobile(ctx: &egui::Context, app: &mut Damus) {
     //let routes = app.timelines[0].routes.clone();
 
     main_panel(&ctx.style(), ui::is_narrow(ctx)).show(ctx, |ui| {
-        if !app.columns.columns().is_empty() && nav::render_nav(0, app, ui) {
+        if !app.columns.columns().is_empty() {
-            storage::save_columns(&app.path, app.columns.as_serializable_columns());
+            if let Some(r) = nav::render_nav(0, app, ui) {
+                r.process_nav_response(&app.path, &mut app.columns)
+            }
         }
     });
 }
@@ -807,12 +809,12 @@ fn timelines_view(ui: &mut egui::Ui, sizes: Size, app: &mut Damus) {
                 );
             });
 
-            let mut columns_changed = false;
+            let mut nav_resp: Option<nav::RenderNavResponse> = None;
             for col_index in 0..app.columns.num_columns() {
                 strip.cell(|ui| {
                     let rect = ui.available_rect_before_wrap();
-                    if nav::render_nav(col_index, app, ui) {
+                    if let Some(r) = nav::render_nav(col_index, app, ui) {
-                        columns_changed = true;
+                        nav_resp = Some(r);
                     }
 
                     // vertical line
@@ -826,8 +828,8 @@ fn timelines_view(ui: &mut egui::Ui, sizes: Size, app: &mut Damus) {
                 //strip.cell(|ui| timeline::timeline_view(ui, app, timeline_ind));
             }
 
-            if columns_changed {
+            if let Some(r) = nav_resp {
-                storage::save_columns(&app.path, app.columns.as_serializable_columns());
+                r.process_nav_response(&app.path, &mut app.columns);
             }
         });
 }

src/nav.rs

@@ -1,11 +1,13 @@
 use crate::{
     account_manager::render_accounts_route,
     app_style::{get_font_size, NotedeckTextStyle},
+    column::Columns,
     fonts::NamedFontFamily,
     notes_holder::NotesHolder,
     profile::Profile,
     relay_pool_manager::RelayPoolManager,
     route::Route,
+    storage::{self, DataPath},
     thread::Thread,
     timeline::{
         route::{render_profile_route, render_timeline_route, AfterRouteExecution, TimelineRoute},
@@ -27,8 +29,28 @@ use egui_nav::{Nav, NavAction, TitleBarResponse};
 use nostrdb::{Ndb, Transaction};
 use tracing::{error, info};
 
-pub fn render_nav(col: usize, app: &mut Damus, ui: &mut egui::Ui) -> bool {
+pub enum RenderNavResponse {
-    let mut col_changed = false;
+    ColumnChanged,
+    RemoveColumn(usize),
+}
+
+impl RenderNavResponse {
+    pub fn process_nav_response(&self, path: &DataPath, columns: &mut Columns) {
+        match self {
+            RenderNavResponse::ColumnChanged => {
+                storage::save_columns(path, columns.as_serializable_columns());
+            }
+
+            RenderNavResponse::RemoveColumn(col) => {
+                columns.delete_column(*col);
+                storage::save_columns(path, columns.as_serializable_columns());
+            }
+        }
+    }
+}
+
+pub fn render_nav(col: usize, app: &mut Damus, ui: &mut egui::Ui) -> Option<RenderNavResponse> {
+    let mut resp: Option<RenderNavResponse> = None;
     let col_id = app.columns.get_column_id_at_index(col);
     // TODO(jb55): clean up this router_mut mess by using Router<R> in egui-nav directly
     let routes = app
@@ -193,14 +215,14 @@ pub fn render_nav(col: usize, app: &mut Damus, ui: &mut egui::Ui) -> bool {
                 pubkey.bytes(),
             );
         }
-        col_changed = true;
+        resp = Some(RenderNavResponse::ColumnChanged)
     } else if let Some(NavAction::Navigated) = nav_response.action {
         let cur_router = app.columns_mut().column_mut(col).router_mut();
         cur_router.navigating = false;
         if cur_router.is_replacing() {
             cur_router.remove_previous_routes();
         }
-        col_changed = true;
+        resp = Some(RenderNavResponse::ColumnChanged)
     }
 
     if let Some(title_response) = nav_response.title_response {
@@ -210,13 +232,12 @@ pub fn render_nav(col: usize, app: &mut Damus, ui: &mut egui::Ui) -> bool {
                 if let Some(timeline) = tl {
                     unsubscribe_timeline(app.ndb(), timeline);
                 }
-                app.columns_mut().delete_column(col);
+                resp = Some(RenderNavResponse::RemoveColumn(col))
-                col_changed = true;
             }
         }
     }
 
-    col_changed
+    resp
 }
 
 fn unsubscribe_timeline(ndb: &Ndb, timeline: &Timeline) {