[glibmm] gmmproc: _WRAP_SIGNAL: Use {} for the default value of detail_name

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 50d92077b154068875882837cac850b337b183d7
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Tue Jan 15 15:09:08 2019 +0100

    gmmproc: _WRAP_SIGNAL: Use {} for the default value of detail_name
    
    See issue #20

 tools/m4/signal.m4 | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---
diff --git a/tools/m4/signal.m4 b/tools/m4/signal.m4
index fa2cd998..f2457998 100644
--- a/tools/m4/signal.m4
+++ b/tools/m4/signal.m4
@@ -28,7 +28,7 @@ $10
 ',dnl detail_name
 $14,0,`dnl
 $10
-  Glib::SignalProxyDetailed<$5`'($6)> signal_$4`'(const Glib::ustring& $13 = Glib::ustring());
+  Glib::SignalProxyDetailed<$5`'($6)> signal_$4`'(const Glib::ustring& $13 = {});
 ',`dnl detail_name and two_signal_methods
 $10
   Glib::SignalProxy<$5`'($6)> signal_$4`'();
@@ -350,4 +350,3 @@ ifelse($8,refreturn,`dnl Assume Glib::wrap() is correct if refreturn is requeste
 ifelse(`$9',,,`#endif // $9
 ')dnl
 _POP()')
-