patch 8.2.2027: Coverity warnts for uninitialized field

Problem:    Coverity warnts for uninitialized field.
Solution:   Set "v_lock".
diff --git a/src/list.c b/src/list.c
index 1a82a34..e75a2a7 100644
--- a/src/list.c
+++ b/src/list.c
@@ -867,6 +867,7 @@
     if (l == NULL)
 	return FAIL;
     tv->v_type = VAR_LIST;
+    tv->v_lock = 0;
     tv->vval.v_list = l;
     if (l1 == NULL)
 	++l->lv_refcount;