patch 8.1.0852: findfile() and finddir() are not properly tested

Problem:    findfile() and finddir() are not properly tested.
Solution:   Extend the test and add more. (Dominique Pelle, closes #3880)
diff --git a/src/version.c b/src/version.c
index 1dc9ad0..3652f43 100644
--- a/src/version.c
+++ b/src/version.c
@@ -784,6 +784,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    852,
+/**/
     851,
 /**/
     850,