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)

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    715,
 /**/
     714,
 /**/