[glabels] Added missing function prototype to header.

[Jim Evins <jimevins src gnome org>]

commit 01c80fc941cf5c8bf0d2b64a6a58cc3b5138f932
Author: Jim Evins <evins snaught com>
Date:   Sun Apr 24 11:32:28 2016 -0400

    Added missing function prototype to header.

 src/prefs-model.h |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/prefs-model.h b/src/prefs-model.h
index 72efa84..10316a1 100644
--- a/src/prefs-model.h
+++ b/src/prefs-model.h
@@ -59,6 +59,7 @@ GType          gl_prefs_model_get_type                      (void) G_GNUC_CONST;
 
 glPrefsModel  *gl_prefs_model_new                           (void);
 
+glPrefsModel  *gl_prefs_model_new_null                      (void);
 
 void           gl_prefs_model_set_units                     (glPrefsModel     *this,
                                                              lglUnits          units);