[meld] patchdialog: Make the side selection radiobuttons actually work

[Kai Willadsen <kaiw src gnome org>]

commit 32d3c48896bc6e16db0144d0a9d5cf01e280ffd0
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Wed Jan 9 07:21:55 2019 +1000

    patchdialog: Make the side selection radiobuttons actually work
    
    It seems like this hasn't worked for half a decade, but it's entirely
    possible that some GTK+ change made our mistake here more obvious.

 meld/patchdialog.py               | 1 +
 meld/resources/ui/patch-dialog.ui | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/meld/patchdialog.py b/meld/patchdialog.py
index c5c4975a..1e9fdc5c 100644
--- a/meld/patchdialog.py
+++ b/meld/patchdialog.py
@@ -74,6 +74,7 @@ class PatchDialog(Gtk.Dialog):
         if key == "font":
             self.textview.modify_font(meldsettings.font)
 
+    @Template.Callback()
     def on_buffer_selection_changed(self, radiobutton):
         if not radiobutton.get_active():
             return
diff --git a/meld/resources/ui/patch-dialog.ui b/meld/resources/ui/patch-dialog.ui
index e8dd3e83..732b2373 100644
--- a/meld/resources/ui/patch-dialog.ui
+++ b/meld/resources/ui/patch-dialog.ui
@@ -126,8 +126,9 @@
                     <property name="can_focus">True</property>
                     <property name="receives_default">False</property>
                     <property name="xalign">0</property>
-                    <property name="active">True</property>
+                    <property name="active">False</property>
                     <property name="draw_indicator">True</property>
+                    <property name="group">left_radiobutton</property>
                     <signal name="toggled" handler="on_buffer_selection_changed" swapped="no"/>
                   </object>
                   <packing>