Kbreakout 4.11.3 loses track of the mouse cursor

[Alex Gould <alexngould@fastmail.fm>]

I noticed that beginning with kbreakout 4.11.3 in testing, it is harder to 
control the game's paddle. It seems possible to move the mouse cursor into 
"dead" areas of the screen, beyond the boundaries of the game world. When this 
is done, moving the mouse side to side no longer moves the paddle, until the 
cursor returns to the live area.