[latexila] Use tepl_application_get_active_main_window()

[Sébastien Wilmet <swilmet src gnome org>]

commit 948c5c564b7acd13558f927ca6c21f1e728ee148
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Sat Oct 14 11:30:17 2017 +0200

    Use tepl_application_get_active_main_window()
    
    But it's more convenient to still return the MainWindow type.
    
    Porting to tepl_application_get_active_main_window() has the benefit to
    test that function in latexila. In the future latexila will rely on
    other Tepl features that will use that function.

 src/latexila_app.vala |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)
---
diff --git a/src/latexila_app.vala b/src/latexila_app.vala
index 2f6d187..6f22801 100644
--- a/src/latexila_app.vala
+++ b/src/latexila_app.vala
@@ -57,13 +57,13 @@ public class LatexilaApp : Gtk.Application
 
     public MainWindow? get_active_main_window ()
     {
-        foreach (Gtk.Window window in get_windows ())
-        {
-            if (window is MainWindow)
-                return window as MainWindow;
-        }
+        Tepl.Application tepl_app = Tepl.Application.get_from_gtk_application (this);
+        Gtk.ApplicationWindow? main_window = tepl_app.get_active_main_window ();
+
+        if (main_window == null)
+            return null;
 
-        return null;
+        return main_window as MainWindow;
     }
 
     private void setup_main_option_entries ()