sftp_packet_require: sftp_packet_read() returning 0 is not an error
sftp_packet_require: sftp_packet_read() returning 0 is not an error

Exactly as the comment in the code said, checking the return code from
sftp_packet_read() with <= was wrong and it should be < 0. With the new
filtering on incoming packets that are "zombies" we can now see this
getting zero returned.

libssh2/libssh2,libssh2/libssh2,libssh2/libssh2,libssh2/libssh2