zip: fix staticcheck errors

Reported by dmitshur in a comment in CL 202042.

Change-Id: I913bd87d9a17a9cf19ac869f8b7166b05e839758
Reviewed-on: https://go-review.googlesource.com/c/mod/+/218237
Run-TryBot: Jay Conrod <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: Jay Conrod

zip/zip.go

@@ -247,6 +247,9 @@ func CreateFromDir(w io.Writer, m module.Version, dir string) (err error) {
 
 	var files []File
 	err = filepath.Walk(dir, func(filePath string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
 		relPath, err := filepath.Rel(dir, filePath)
 		if err != nil {
 			return err

zip/zip_test.go

@@ -89,7 +89,7 @@ func (f fakeFile) Open() (io.ReadCloser, error) {
 	if f.data != nil {
 		return ioutil.NopCloser(bytes.NewReader(f.data)), nil
 	}
-	if f.size < 0 || f.size >= uint64(modzip.MaxZipFile<<1) {
+	if f.size >= uint64(modzip.MaxZipFile<<1) {
 		return nil, fmt.Errorf("cannot open fakeFile of size %d", f.size)
 	}
 	return ioutil.NopCloser(io.LimitReader(zeroReader{}, int64(f.size))), nil