fix : show the right frame when a call ends.

- returns to the welcome page if no contact is selected during the
end of the call. Returns to the text message page otherwise.

Change-Id: I817a8466b1c5f6725f02c94e2e0d4a678f2878e8
Tuleap: #1056

MainPage.xaml.cpp

@@ -82,7 +82,13 @@ MainPage::MainPage()
         showFrame(_videoFrame_);
     });
     CallsViewModel::instance->callEnded += ref new CallEnded([&]() {
+        auto contact = ContactsViewModel::instance->selectedContact;
+
+        if(contact)
             showFrame(_messageTextFrame_);
+        else
+            showFrame(_welcomeFrame_);
+
     });
 
     DisplayInformation^ displayInformation = DisplayInformation::GetForCurrentView();