Fix a couple of warnings relating to parents of dialogs

Fixes these kind of warnings:
```
(dino:<PID>): Gtk-CRITICAL **: gtk_window_set_transient_for: assertion 'parent == NULL || GTK_IS_WINDOW (parent)' failed
Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.
(dino:<PID>): GLib-GObject-WARNING **: invalid cast from 'GtkPaned' to 'GtkWindow'
```

Also centers these dialogs (settings, add chat, join conversation) on
top of their parent windows.

1 files changed, 3 insertions, 3 deletions

diff --git a/main/src/ui/conversation_list_titlebar.vala b/main/src/ui/conversation_list_titlebar.vala
index 5ef824d5..c49b43c4 100644
--- a/main/src/ui/conversation_list_titlebar.vala
+++ b/main/src/ui/conversation_list_titlebar.vala
@@ -23,7 +23,7 @@ public class ConversationListTitlebar : Gtk.HeaderBar {
         SimpleAction contacts_action = new SimpleAction("add_chat", null);
         contacts_action.activate.connect(() => {
             AddConversation.Chat.Dialog add_chat_dialog = new AddConversation.Chat.Dialog(stream_interactor);
-            add_chat_dialog.set_transient_for((Window) get_toplevel());
+            add_chat_dialog.set_transient_for(window);
             add_chat_dialog.conversation_opened.connect((conversation) => conversation_opened(conversation));
             add_chat_dialog.show();
         });
@@ -32,7 +32,7 @@ public class ConversationListTitlebar : Gtk.HeaderBar {
         SimpleAction conference_action = new SimpleAction("add_conference", null);
         conference_action.activate.connect(() => {
             AddConversation.Conference.Dialog add_conference_dialog = new AddConversation.Conference.Dialog(stream_interactor);
-            add_conference_dialog.set_transient_for((Window) get_toplevel());
+            add_conference_dialog.set_transient_for(window);
             add_conference_dialog.conversation_opened.connect((conversation) => conversation_opened(conversation));
             add_conference_dialog.show();
         });
@@ -44,4 +44,4 @@ public class ConversationListTitlebar : Gtk.HeaderBar {
     }
 }
 
-}
\ No newline at end of file
+}