patch 8.2.0571: double free when passing invalid argument to job_start()

Problem:    Double free when passing invalid argument to job_start().
Solution:   Clear the argument when freed. (Masato Nishihata, closes #5926)
diff --git a/src/version.c b/src/version.c
index df1dcec..40e048d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    571,
+/**/
     570,
 /**/
     569,