[geary] Fix messages not being auto-marked read on scroll.

[Michael Gratton <mjog src gnome org>]

commit 485b8c8598adee4c4d0e436d6e9a48b685b614b6
Author: Michael James Gratton <mike vee net>
Date:   Sat Mar 4 14:05:20 2017 +1100

    Fix messages not being auto-marked read on scroll.
    
    Fixes bug introduced by commit 07966a1.
    
    * src/client/conversation-viewer/conversation-viewer.vala
      (ConversationViewer::load_conversation): Remove old conversation before
      loading the new one, so the list box picks up the new scrolled window's
      hadjustment rather than the old one.

 .../conversation-viewer/conversation-viewer.vala   |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/client/conversation-viewer/conversation-viewer.vala 
b/src/client/conversation-viewer/conversation-viewer.vala
index 8ddfb0e..b8361a9 100644
--- a/src/client/conversation-viewer/conversation-viewer.vala
+++ b/src/client/conversation-viewer/conversation-viewer.vala
@@ -185,6 +185,8 @@ public class ConversationViewer : Gtk.Stack {
     public async void load_conversation(Geary.App.Conversation conversation,
                                         Geary.Folder location)
         throws Error {
+        remove_current_list();
+
         Geary.Account account = location.account;
         ConversationListBox new_list = new ConversationListBox(
             conversation,
@@ -221,7 +223,6 @@ public class ConversationViewer : Gtk.Stack {
             new_list.highlight_search_terms(find_terms);
         }
 
-        remove_current_list();
         add_new_list(new_list);
         set_visible_child(this.conversation_page);