move lastReadId forward after sending message;
move lastReadId forward after sending message;

also prevent lastReadId from going backwards.

notbakaneko/osu-web,ppy/osu-web,omkelderman/osu-web,ppy/osu-web,omkelderman/osu-web,LiquidPL/osu-web,notbakaneko/osu-web,LiquidPL/osu-web,nanaya/osu-web,notbakaneko/osu-web,ppy/osu-web,notbakaneko/osu-web,LiquidPL/osu-web,LiquidPL/osu-web,nanaya/osu-web,ppy/osu-web,notbakaneko/osu-web,nanaya/osu-web,omkelderman/osu-web,nanaya/osu-web,ppy/osu-web,omkelderman/osu-web,nanaya/osu-web,LiquidPL/osu-web