Bug 797295 - problems with entering swedish åäö in company address

scm_c_string_length() returns the wrong answer when the C string is
UTF8: It returns the number of codepoints because the SCM string is in
UTF32, but we need the number of bytes for gtk_text_buffer_set_text.
Fortunately scm_to_utf8_string returns a null-terminated string so
we can just tell gtk_text_buffer_set_text to figure it out on its own.

Guile doesn't use g_malloc so don't use g_free, and gpointer* is a
void** so change the cast to void* for free.

gnucash/gnome-utils/dialog-options.c

@@ -3235,8 +3235,8 @@ gnc_option_set_ui_value_text (GNCOption *option, gboolean use_default,
         const gchar *string;
 
         string = gnc_scm_to_utf8_string (value);
-        gtk_text_buffer_set_text (buffer, string, scm_c_string_length(value));
-        g_free ((gpointer *) string);
+        gtk_text_buffer_set_text (buffer, string, -1);
+        free ((void*) string);
         return FALSE;
     }
     else