[gtk/prop-list] builder: Avoid another critical

[Matthias Clasen <matthiasc src gnome org>]

commit c18ff40910be9876a7c7601d3b1257ff15c4fe85
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon Dec 23 16:14:27 2019 -0500

    builder: Avoid another critical
    
    Only free an expression if we managed
    to create one.

 gtk/gtkbuilderparser.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gtk/gtkbuilderparser.c b/gtk/gtkbuilderparser.c
index 6ba536dd58..f7a323b508 100644
--- a/gtk/gtkbuilderparser.c
+++ b/gtk/gtkbuilderparser.c
@@ -1042,7 +1042,7 @@ free_expression_info (ExpressionInfo *info)
   switch (info->expression_type)
     {
     case EXPRESSION_EXPRESSION:
-      gtk_expression_unref (info->expression);
+      g_clear_pointer (&info->expression, gtk_expression_unref);
       break;
 
     case EXPRESSION_CONSTANT: