Replace the temporary CRC working buffer in `LDPC::ft8_crc()` with a
`std::vector<int>`.
The vector is value-initialized, preserving the existing zero-padding
behavior, while `std::memcpy()` copies the input message into the front
of the buffer. This removes the manual `malloc()`/`free()` pair, simplifies
the implementation, and uses RAII for temporary storage.
This change also addresses a cppcheck warning about a possible null pointer
dereference following malloc() failure. If memory allocation now fails,
std::vector will throw std::bad_alloc rather than returning a null pointer
that would be dereferenced. The algorithm and behavior are otherwise
unchanged.
Signed-off-by: Robin Getz <rgetz503@gmail.com>