patch 8.2.3396: when libcall() fails invalid pointer may be used

Problem:    When libcall() fails invalid pointer may be used.
Solution:   Initialize the string to NULL. (Yasuhiro Matsumoto, closes #8829)
diff --git a/src/version.c b/src/version.c
index 435affe..3708e8f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3396,
+/**/
     3395,
 /**/
     3394,