patch 8.2.2820: session file may divide by zero

Problem:    Session file may divide by zero.
Solution:   Avoid writing difide by zero. (closes #8162)
diff --git a/src/version.c b/src/version.c
index b1ba0a1..ed632f7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2820,
+/**/
     2819,
 /**/
     2818,