Fix ASCIIHexDecode: convert binary input string to ascii string.

[sklaw]

Otherwise, 'not in' and 'rstrip' would fail.

[sklaw]

This patch fixes the following error:

python3.7 pdf-parser.py /home/test/.msf4/local/msf.pdf --object 6 --filter --overridingfilters="/FlateDecode /ASCIIHexDecode" --raw
This program has not been tested with this version of Python (3.7.10)
Should you encounter problems, please use Python version 3.7.5
obj 6 0
 Type: 
 Referencing: 
 Contains stream

  <<
    /Length 4930
    /Filter [/#46lat#65#44ecod#65/AS#43#49#49#48#65#78Dec#6f#64#65]
  >>

 ASCIIHexDecode decompress failed

where msf.pdf is generated by metasploit exploit/windows/fileformat/adobe_utilprintf