patch 8.0.0663: unexpected error message only when 'verbose' is set

Problem:    Giving an error message only when 'verbose' set is unexpected.
Solution:   Give a warning message instead.
diff --git a/src/version.c b/src/version.c
index ab7a929..102e388 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    663,
+/**/
     662,
 /**/
     661,