get next line with only 1 byte reachable by valgirnd

==58252== ==58252== HEAP SUMMARY: ==58252== in use at exit: 1 bytes in 1 blocks ==58252== total heap usage: 514 allocs, 513 frees, 162,302 bytes allocated ==58252== ==58252== 1 bytes in 1 blocks are still reachable in loss record 1 of 1 ==58252== at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so) ==58252== by 0x109799: ft_strdup (in /home/ds/42/gnl-tests_04/a.out) ==58252== by 0x109612: ft_formbox (in /home/ds/42/gnl-tests_04/a.out) ==58252== by 0x10926B: get_next_line (in /home/ds/42/gnl-tests_04/a.out) ==58252== by 0x109AF4: main (in /home/ds/42/gnl-tests_04/a.out) ==58252== ==58252== LEAK SUMMARY: ==58252== definitely lost: 0 bytes in 0 blocks ==58252== indirectly lost: 0 bytes in 0 blocks ==58252== possibly lost: 0 bytes in 0 blocks ==58252== still reachable: 1 bytes in 1 blocks ==58252== suppressed: 0 bytes in 0 blocks ==58252== ==58252== For lists of detected and suppressed errors, rerun with: -s ==58252== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)