patch 9.0.0975: virtual text below empty line misplaced when 'number' set

Problem:    Virtual text below an empty line is misplaced when 'number' is
            set.
Solution:   Adjust the computations. (closes #11629)

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    975,
 /**/
     974,
 /**/