[geary] Downgrade sidebar warning message to debug to ease debugging

[Michael Gratton <mjog src gnome org>]

commit c2a719210a2c218e747d1a1bbd3d953db189a4d8
Author: Michael Gratton <mike vee net>
Date:   Sun Oct 14 12:06:44 2018 +1100

    Downgrade sidebar warning message to debug to ease debugging
    
    This get triggered a lot on close, which is annoying when running under
    a debugger with G_DEBUG=fatal-warnings set.

 src/client/sidebar/sidebar-tree.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/client/sidebar/sidebar-tree.vala b/src/client/sidebar/sidebar-tree.vala
index a657fa32..180c98fa 100644
--- a/src/client/sidebar/sidebar-tree.vala
+++ b/src/client/sidebar/sidebar-tree.vala
@@ -206,7 +206,7 @@ public class Sidebar.Tree : Gtk.TreeView {
     private EntryWrapper? get_wrapper(Sidebar.Entry entry) {
         EntryWrapper? wrapper = entry_map.get(entry);
         if (wrapper == null)
-            warning("Entry %s not found in sidebar", entry.to_string());
+            debug("Entry %s not found in sidebar", entry.to_string());
         
         return wrapper;
     }