Validate date in _fixup_recurrence_start_dates, #443941 win32 crash.

This invalid date is due to a missing block <fs:once> in the data file.
Why there is such an unwanted and incomplete sx is still unclear.


git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@16214 57a11ea4-9604-0410-9ed3-97b8803252fd

src/backend/file/gnc-schedxaction-xml-v2.c

@@ -453,6 +453,7 @@ _fixup_recurrence_start_dates(GDate *sx_start_date, GList *schedule)
         g_date_clear(&next, 1);
 
         recurrenceNextInstance(r, &start, &next);
+        g_return_if_fail(g_date_valid(&next));
 
         {
             gchar date_str[128];