[geary/wip/430-custom-window-buttons] Fix handling GTK button-layout settings that are missing a ':'

[Michael Gratton <mjog src gnome org>]

commit ca6d5fdc883d193966fbd9eacd3ec448cb0c0a69
Author: Michael Gratton <mike vee net>
Date:   Wed Jul 17 16:38:02 2019 +1000

    Fix handling GTK button-layout settings that are missing a ':'
    
    See #430

 src/client/components/main-toolbar.vala | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)
---
diff --git a/src/client/components/main-toolbar.vala b/src/client/components/main-toolbar.vala
index c7ab8273..3dc590eb 100644
--- a/src/client/components/main-toolbar.vala
+++ b/src/client/components/main-toolbar.vala
@@ -118,14 +118,14 @@ public class MainToolbar : Gtk.Box {
 
     private void set_window_buttons() {
         string[] buttons = Gtk.Settings.get_default().gtk_decoration_layout.split(":");
-        if (buttons.length != 2) {
-            warning("gtk_decoration_layout in unexpected format");
-            return;
-        }
-        show_close_button_left = show_close_button;
-        show_close_button_right = show_close_button;
-        folder_header.decoration_layout = buttons[0] + ":";
-        conversation_header.decoration_layout = ":" + buttons[1];
+        this.show_close_button_left = this.show_close_button;
+        this.show_close_button_right = this.show_close_button;
+        this.folder_header.decoration_layout = buttons[0] + ":";
+        this.conversation_header.decoration_layout = (
+            (buttons.length == 2)
+            ? ":" + buttons[1]
+            : ""
+        );
     }
 
     // Updates tooltip text depending on number of conversations selected.