Fix decryption failed issue by nonce overwrite

If the first packet is less than nonce length, then the chunk nonce data will be overwrote by next packet and result in decrypt failed

src/stream.c

@@ -493,7 +493,7 @@ stream_decrypt(buffer_t *ciphertext, cipher_ctx_t *cipher_ctx, size_t capacity)
                               ciphertext->len);
 
         if (left_len > 0) {
-            memcpy(cipher_ctx->chunk->data, ciphertext->data, left_len);
+            memcpy(cipher_ctx->chunk->data + cipher_ctx->chunk->len, ciphertext->data, left_len);
             memmove(ciphertext->data, ciphertext->data + left_len,
                     ciphertext->len - left_len);
             cipher_ctx->chunk->len += left_len;