patch 8.2.0403: when 'buftype' is "nofile" there is no overwrite check

Problem:    When 'buftype' is "nofile" there is no overwrite check.
Solution:   Also check for existing file when 'buftype' is set.
            (closes #5807)
diff --git a/src/version.c b/src/version.c
index c76d312..83feed9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    403,
+/**/
     402,
 /**/
     401,