crypt: fix hash mismatches with no_data_encryption on backends which check upload hashes

Before this change, when no_data_encryption was set, uploads from
local disk advertised the hash of the encrypted data even though the
data was uploaded unencrypted.

On backends which check upload hashes (eg b2) this made uploads of
small files fail with errors like "Checksum did not match data
received", and made chunked uploads store an incorrect hash so the
files failed their checksum on download with "corrupted on transfer:
SHA1 hashes differ".

See: https://forum.rclone.org/t/sha1-mismatches-on-b2-with-no-data-encryption-true/54121

backend/crypt/crypt.go

@@ -1179,6 +1179,11 @@ func (o *ObjectInfo) Size() int64 {
 // Hash returns the selected checksum of the file
 // If no checksum is available it returns ""
 func (o *ObjectInfo) Hash(ctx context.Context, hash hash.Type) (string, error) {
+	// If the data is unchanged then the hash of the source is the
+	// hash of the object which will be uploaded
+	if o.f.opt.NoDataEncryption {
+		return o.ObjectInfo.Hash(ctx, hash)
+	}
 	var srcObj fs.Object
 	var ok bool
 	// Get the underlying object if there is one

backend/crypt/crypt_internal_test.go

@@ -84,6 +84,10 @@ func testObjectInfo(t *testing.T, f *Fs, wrap bool) {
 
 	// Test ObjectInfo.Hash
 	wantHash := md5.Sum(outBuf.Bytes())
+	if f.opt.NoDataEncryption {
+		// If the data isn't encrypted, the hash should be that of the plaintext
+		wantHash = md5.Sum([]byte(contents))
+	}
 	gotHash, err := src.Hash(ctx, hash.MD5)
 	require.NoError(t, err)
 	assert.Equal(t, fmt.Sprintf("%x", wantHash), gotHash)