trees-plugin.c

Tomasz Miąsko reported multiple issues with the trees_read_line_fd using
the trees_password_fd field. It is currently unused which used to be
used by the unit tests and dovadm in the Posteo scrambler plugin.

The issues are:

    In trees_read_line_fd(), this check is bad:

        if (bytes_read > MAXIMAL_PASSWORD_LENGTH)

    Currently it is incorrect because when "bytes_read >
    MAXIMAL_PASSWORD_LENGTH" is true, then buffer capacity is already
    exceeded (or just right if you take into account one byte slack
    allocated in str_new for terminating null). Moreover, the buffer
    will be overrun by one more byte in "pointer[0] = 0;" after leaving
    the loop.

Reported-by: Tomasz Miąsko <tomasz.miasko@gmail.com>
Signed-off-by: David Goulet <dgoulet@riseup.net>