patch 8.1.0716: get warning message when 'completefunc' returns nothing

Problem:    Get warning message when 'completefunc' returns nothing.
Solution:   Allow for returning v:none to suppress the warning message.
            (Yasuhiro Matsumoto, closes #3789)
diff --git a/src/version.c b/src/version.c
index eb55daf..9fffc2a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -800,6 +800,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    716,
+/**/
     715,
 /**/
     714,