patch 9.0.1166: code is indented more than necessary

Problem:    Code is indented more than necessary.
Solution:   Use an early return where it makes sense. (Yegappan Lakshmanan,
            closes #11792)
diff --git a/src/fold.c b/src/fold.c
index 61bffb5..589727d 100644
--- a/src/fold.c
+++ b/src/fold.c
@@ -516,7 +516,7 @@
     if (*p_fcl == NUL)
 	return;
 
-    // can only be "all" right now
+    // 'foldclose' can only be "all" right now
     checkupdate(curwin);
     if (checkCloseRec(&curwin->w_folds, curwin->w_cursor.lnum,
 		(int)curwin->w_p_fdl))