Fix Encode error

[finn79426]

Tested under: Python 3.7.3 & 3.9.5

>$ iosgrep.py keywords.txt .

---use plaintext to search---

# grep -ril -e 'foobar'  . :
Find
------
---use hex to search---

# grep -ril -e '666f6f626172'  . :
Not Found
------
---use base64 to search---

# grep -ril -e 'Zm9vYmFy'  . :
Not Found
------
---use md5 to search---

# grep -ril -e '3858f62230ac3c915f300c664312c63f'  . :
Not Found
------
---use sha1 to search---

# grep -ril -e '8843d7f92416211de9ebb963ff4ce28125932878'  . :
Not Found
------
---use utf-8 to search---

# grep -ril -e 'foobar'  . :
Find
------
---use binary to search---

# grep -ril -e '1100110\s1101111\s1101111\s1100010\s1100001\s1110010'  . :
Not Found
------
---use unicode to search---
# grep -ril -e 'foobar'  . :
Find
------