xterm-addon-serialize does not preserve empty cell background

[mmis1000]

Details

• Browser and browser version: any(not browser issue)
• OS version: mac
• xterm.js version: 003cf96
• xterm-addon-serialize version: 003cf96

Steps to reproduce

1. open the demo
2. run echo -e '\x1B[0;37;44mHI2\x1b[10X\x1b[m'
3. check the Write back to terminaloption of SerializeAddon
4. click Serialize the content of terminal
5. Notice the background of empty cell is gone

Note

Also observed when do this on htop