patch 8.2.4627: flatten() does not use maxdepth correctly

Problem:    flatten() does not use maxdepth correctly.
Solution:   Use a recursive implementation. (closes #10020)
diff --git a/src/version.c b/src/version.c
index c13d03f..e292626 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4627,
+/**/
     4626,
 /**/
     4625,