convert dll name to printable characters

If a sample has a invalid utf8 character in the DLL import it will cause JSONDump and MongoDB reporting to not error out.  This change will drop the invalid utf8 character.

The dll name I ran across had "\x97" in the import section.

JSONDump error
UnicodeDecodeError: 'utf8' codec can't decode byte 0x97 in position 12: invalid start byte

MongoDB error:
UnicodeDecodeError: 'utf8' codec can't decode byte 0x97 in position 12: invalid start byte