If the InputStream has less than 4 (OOXML less than 8) bytes and is wrapped into a PushbackInputStream, the data in this PushbackInputStream gets corrupted.

Background:
Both methods try to read 4 (OOXML 8) bytes from the stream into a buffer and then push back this buffer. But these methods always push back the entire buffer, no matter how many bytes have actually been read from the stream. In the case that the stream contains less than 4 (OOXML 8) bytes, the PushbackInputStream is now extended to 4 (8) bytes with 0x00s.

This patch records the actual nember of bytes read from the stream only only pushes back this ammount of bytes.