server: Simplify the MJPEG encoder's maximum framerate estimation
server: Simplify the MJPEG encoder's maximum framerate estimation

Note that if frame_size == bytes_per_sec == 0 this now returns
MJPEG_MAX_FPS but this should not happen anyway.

Signed-off-by: Francois Gouget <6b915da68578f6eb004fe99432b967565fc9be8f@codeweavers.com>

fgouget/spice,fgouget/spice,SPICE/spice,fgouget/spice,fgouget/spice,SPICE/spice,SPICE/spice