archive/zip: only consider UncompressedSize when checking dirs

CL 454475 switched from checking CompressedSize to UncompressedSize
when determining if we should consider an archive malformed because
it contains data and added a test for an example of this (a JAR). We
should also remove the hasDataDescriptor check, since that is basically
an alias for CompressedSize > 0. The test didn't catch this because we
didn't actually attempt to read from the returned reader.

Change-Id: Ibc4c1aa9c3a733f3ebf4a956d1e2f8f4900a29cd
Reviewed-on: https://go-review.googlesource.com/c/go/+/455523
Run-TryBot: Roland Shoemaker <roland@golang.org>
Reviewed-by: Julie Qiu <julieqiu@google.com>
Auto-Submit: Roland Shoemaker <roland@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/archive/zip/reader.go

@@ -237,7 +237,7 @@ func (f *File) Open() (io.ReadCloser, error) {
 		// 0. We still want to fail when a directory has associated uncompressed
 		// data, but we are tolerant of cases where the uncompressed size is
 		// zero but compressed size is not.
-		if f.UncompressedSize64 != 0 || f.hasDataDescriptor() {
+		if f.UncompressedSize64 != 0 {
 			return &dirReader{ErrFormat}, nil
 		} else {
 			return &dirReader{io.EOF}, nil

src/archive/zip/reader_test.go

@@ -1702,9 +1702,12 @@ func TestCompressedDirectory(t *testing.T) {
 		t.Fatalf("unexpected error: %v", err)
 	}
 	for _, f := range r.File {
-		_, err = f.Open()
+		r, err := f.Open()
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
 		}
+		if _, err := io.Copy(io.Discard, r); err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
 	}
 }