TextWidget should set dirty region in setText function.

frontend/ui/widget/textwidget.lua

@@ -1,3 +1,4 @@
+local UIManager = require("ui/uimanager")
 local Widget = require("ui/widget/widget")
 local Screen = require("device").screen
 local RenderText = require("ui/rendertext")
@@ -50,6 +51,7 @@ end
 function TextWidget:setText(text)
     self.text = text
     self:updateSize()
+    UIManager:setDirty(self, "partial")
 end
 
 function TextWidget:paintTo(bb, x, y)