return to caller when there is no window to show in UIManager
set refresh type on eink update in fillMxcfbUpdateData
add more comments
adapt refresh type code in fillMxcfbUpdateData

just to keep consistent with the old refresh type, i.e.
0 for full refresh and 1 for partial
Merge pull request #696 from houqp/new_ui_fix

set refresh type on eink update in fillMxcfbUpdateData
Merge pull request #695 from houqp/new_ui_houqp

return to caller when there is no window to show in UIManager