patch 8.1.0574: 'commentstring' not used when adding fold marker in C

Problem:    'commentstring' not used when adding fold marker in C.
Solution:   Require white space before middle comment part. (mostly by
            Hirohito Higashi)
diff --git a/src/version.c b/src/version.c
index 880a510..45d1858 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    574,
+/**/
     573,
 /**/
     572,