patch 9.0.0837: append() reports failure when not appending anything

Problem:    append() reports failure when not appending anything.
Solution:   Only report failure when appending something. (closes #11498)

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    837,
 /**/
     836,
 /**/