Make sure the viewport is filled when reflowing a row change
Make sure the viewport is filled when reflowing a row change

Fixes #1926

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