[gnumeric] Style: fix crash on exit.

[Morten Welinder <mortenw src gnome org>]

commit a069dde2f704815bef674e9fc6a49d501f8afcc5
Author: Morten Welinder <terra gnome org>
Date:   Tue Mar 26 09:51:29 2013 -0400

    Style: fix crash on exit.

 src/mstyle.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/src/mstyle.c b/src/mstyle.c
index a17d38b..0ab8899 100644
--- a/src/mstyle.c
+++ b/src/mstyle.c
@@ -549,7 +549,10 @@ gnm_style_clear_pango (GnmStyle *style)
 static inline void
 gnm_style_clear_font (GnmStyle *style)
 {
-       g_clear_object (&style->font);
+       if (style->font) {
+               gnm_font_unref (style->font);
+               style->font = NULL;
+       }
        g_clear_object (&style->font_context);
 }