patch 9.0.0715: wrong argument for append() gives two error messages

Problem:    Wrong argument for append() gives two error messages.
Solution:   When getting an error for a number argument don't try using it as
            a string. (closes #11335)
diff --git a/src/version.c b/src/version.c
index 772267e..564d69d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    715,
+/**/
     714,
 /**/
     713,