Fix some lengths in crypt()

    Use salt_len_in instead of strlen(salt) or PHP_MAX_SALT_LEN, otherwise too
    much memory will be allocated.

    sha512 has a 86 character checksum, not 43. That probably was a copy&paste
    from the sha256 code which indeed has 43.

    The allocation also were using sizeof(char *) instead of sizeof(char), thus
    allocating 4 or 8 times as much memory as necessary.

    The memset 0 call was using PHP_MAX_SALT_LEN which can be smaller then the
    output buffer and thus not zeroing out everything. Use the size of the
    output buffer (needed) instead.