patch 8.0.0170: crash in channel test

Problem:    Channel test fails for using freed memory.
Solution:   Fix memory use in json_decode().
diff --git a/src/json.c b/src/json.c
index 091d98f..2cc3a2a 100644
--- a/src/json.c
+++ b/src/json.c
@@ -577,6 +577,8 @@
     ga_init2(&stack, sizeof(json_dec_item_T), 100);
     cur_item = res;
     init_tv(&item);
+    if (res != NULL)
+    init_tv(res);
 
     fill_numbuflen(reader);
     p = reader->js_buf + reader->js_used;
@@ -985,7 +987,6 @@
 
 theend:
     ga_clear(&stack);
-    clear_tv(&item);
     return retval;
 }
 
diff --git a/src/version.c b/src/version.c
index 23dd5ae..4bc287f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    170,
+/**/
     169,
 /**/
     168,