[geary/mjog/composer-fixes: 2/2] Composer.Widget: Fix critical when immediately detaching a new composer

[Michael Gratton <mjog src gnome org>]

commit 70186163e8bcf1a0644669fe7c9b2b56dceef9b5
Author: Michael Gratton <mike vee net>
Date:   Sun Sep 27 22:46:40 2020 +1000

    Composer.Widget: Fix critical when immediately detaching a new composer
    
    New composers have no associated GLib Application instance, so when the
    main window is already showing a composer and another is opened, the
    new composer has no application to pass its window.
    
    Fix by requiring `Composer.detach` be passed an application instance
    and find an appropriate instance at each call site.

 src/client/application/application-main-window.vala | 2 +-
 src/client/composer/composer-widget.vala            | 6 ++----
 2 files changed, 3 insertions(+), 5 deletions(-)
---
diff --git a/src/client/application/application-main-window.vala 
b/src/client/application/application-main-window.vala
index e8428459c..73b50e335 100644
--- a/src/client/application/application-main-window.vala
+++ b/src/client/application/application-main-window.vala
@@ -875,7 +875,7 @@ public class Application.MainWindow :
      */
     internal void show_composer(Composer.Widget composer) {
         if (this.has_composer) {
-            composer.detach();
+            composer.detach(this.application);
         } else {
             // See if the currently displayed conversation contains
             // any of the composer's referred emails (preferring the
diff --git a/src/client/composer/composer-widget.vala b/src/client/composer/composer-widget.vala
index dab8cfd88..37e93fb43 100644
--- a/src/client/composer/composer-widget.vala
+++ b/src/client/composer/composer-widget.vala
@@ -785,10 +785,8 @@ public class Composer.Widget : Gtk.EventBox, Geary.BaseInterface {
     }
 
     /** Detaches the composer and opens it in a new window. */
-    public void detach() {
+    public void detach(Application.Client application) {
         Gtk.Widget? focused_widget = null;
-        var application = this.container.top_window.application as Application.Client;
-
         if (this.container != null) {
             focused_widget = this.container.top_window.get_focus();
             this.container.close();
@@ -2374,7 +2372,7 @@ public class Composer.Widget : Gtk.EventBox, Geary.BaseInterface {
     }
 
     private void on_detach() {
-        detach();
+        detach(this.container.top_window.application as Application.Client);
     }
 
     private void on_add_attachment() {