Fix off-by ones in UTF-8 parsing in terminal

- 11100000 (224) was misinterpreted as 2-byte sequence, whereas it defines a 3-byte
- 11110000 (240) was misinterpreted as 3-byte sequence, whereas it defines a 4-byte

Makes it possible to type characters from the Supplementary Multilingual Plane such as 𐎒 and 𝄐.