zstd: fix crash in decoding

[WojciechMula]

Fixes #562 and #563.

[WojciechMula]

The file causes also some problems in Go code. For invocation go test -tags noasm -run TestDecoderRegression we have:

--- FAIL: TestDecoderRegression (0.24s)
    --- FAIL: TestDecoderRegression/Reader-05d57667c86a14c61262c925d95d398c6e921012 (0.00s)
        decoder_test.go:671: Received: 56821 output (177670) bigger than max block size (45056)
        decoder_test.go:686: Fresh Reader received: 56821 output (165905) bigger than max block size (45056)
        decoder_test.go:689: output (177670) bigger than max block size (45056) != output (165905) bigger than max block size (45056)

[klauspost]

You can add this to fix the Go code:

diff --git a/zstd/seqdec.go b/zstd/seqdec.go
index 477b1e1..a635f84 100644
--- a/zstd/seqdec.go
+++ b/zstd/seqdec.go
@@ -299,7 +299,7 @@ func (s *sequenceDecs) decodeSync(hist []byte) error {
 		}
 		size := ll + ml + len(out)
 		if size-startSize > maxBlockSize {
-			return fmt.Errorf("output (%d) bigger than max block size (%d)", size, maxBlockSize)
+			return fmt.Errorf("output (%d) bigger than max block size (%d)", size-startSize, maxBlockSize)
 		}
 		if size > cap(out) {
 			// Not enough size, which can happen under high volume block streaming conditions
@@ -410,7 +410,7 @@ func (s *sequenceDecs) decodeSync(hist []byte) error {
 
 	// Check if space for literals
 	if len(s.literals)+len(s.out)-startSize > maxBlockSize {
-		return fmt.Errorf("output (%d) bigger than max block size (%d)", len(s.out), maxBlockSize)
+		return fmt.Errorf("output (%d) bigger than max block size (%d)", len(s.literals)+len(s.out)-startSize, maxBlockSize)
 	}
 
 	// Add final literals

[WojciechMula]

You can add this to fix the Go code:

Thank you very much! It helped.