Do not stop after 79 characters. Read the complete line to avoid
arbitrary limitations.
Proof of Concept:
```
cat > passwd-poc << EOF
root❌0:0:root:/root:/bin/bash
root❌0:0:root:/root:/bin/bash
root❌0:0:root:/root:/bin/bash
EOF
python -c "print(80*'y')" | pwck passwd-poc
```
Two lines should still be within the file because we agreed only once
to remove a duplicated line.
Signed-off-by: Samanta Navarro <ferivoz@riseup.net>
Reviewed-by: Alejandro Colomar <alx@kernel.org>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
0c83b98105