vfmt: keep top level comments on their own lines

vlib/v/fmt/fmt.v

@@ -1080,7 +1080,7 @@ pub fn (mut f Fmt) comment(node ast.Comment) {
 		} else {
 			s = '// ' + s
 		}
-		if !is_separate_line {
+		if !is_separate_line && f.indent > 0 {
 			f.remove_new_line() // delete the generated \n
 			f.write(' ')
 		}