Buffer overread in rm2fb client

[matteodelabre]

There is a buffer overread in the following call to msgsnd:

vnsee/src/rmioc/screen_rm2fb.cpp

Line 165 in 6ed9593

if (msgsnd(this->msgqueue_id, &message, sizeof(message), 0) == -1)

As per the man page, the msgsz argument (third argument) should not include the size of the mtype field, only of the data field, so currently this call will read 4 extra bytes from memory and send them to the server.

(Related to ddvk/remarkable2-framebuffer#89.)