path/filepath: add explicit comment marking elided errors

The errors on these lines are meant to be discarded.
Add a comment to make that extra clear.

Change-Id: I38f72af6dfbb0e86677087baf47780b3cc6e7d40
Reviewed-on: https://go-review.googlesource.com/c/go/+/241083
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/path/filepath/match.go b/src/path/filepath/match.go
index 46badb5..20a3348 100644
--- a/src/path/filepath/match.go
+++ b/src/path/filepath/match.go
@@ -310,14 +310,14 @@
 	m = matches
 	fi, err := os.Stat(dir)
 	if err != nil {
-		return
+		return // ignore I/O error
 	}
 	if !fi.IsDir() {
-		return
+		return // ignore I/O error
 	}
 	d, err := os.Open(dir)
 	if err != nil {
-		return
+		return // ignore I/O error
 	}
 	defer d.Close()