Two RFB protocol bugs in the /screen client:
1. ServerInit parsed framebuffer-height from byte offset 1 instead of
2. RFB 3.8 ServerInit is width@0-1, height@2-3; u16be(b,1) mixes
the low byte of width with the high byte of height. The wrong
height went into the initial non-incremental FramebufferUpdate-
Request; neatvnc feeds the client's width/height straight into
pixman_region_union_rect un-clipped (src/server.c), so an
out-of-range height corrupts the server damage region and pixman
reports 'Invalid rectangle passed'.
2. FramebufferUpdate handler had a stray drainTo(1) after the 3-byte
padding+nRects header, consuming the first byte of the first
rectangle and desyncing every update.
Closes#128
a5ef10c10c