patch 8.2.0825: def_function() may return pointer that was freed

Problem:    def_function() may return pointer that was freed.
Solution:   Set "fp" to NULL after freeing it.
diff --git a/src/version.c b/src/version.c
index ce5f627..5ccbfad 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    825,
+/**/
     824,
 /**/
     823,