Ensure leave is called when leaving a MouseZone
Ensure leave is called when leaving a MouseZone

Fixes #975

xtermjs/xterm.js,Tyriar/xterm.js,akalipetis/xterm.js,xtermjs/xterm.js,sourcelair/xterm.js,Tyriar/xterm.js,akalipetis/xterm.js,xtermjs/xterm.js,akalipetis/xterm.js,Tyriar/xterm.js,xtermjs/xterm.js,sourcelair/xterm.js,Tyriar/xterm.js,xtermjs/xterm.js,sourcelair/xterm.js,akalipetis/xterm.js,sourcelair/xterm.js,Tyriar/xterm.js