app/internal/windows: don't draw window background on Windows

Avoids flickering between GPU content and the CPU drawn background
color.

gofmt -w -s . now we're here.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

widget/material/material.go

@@ -24,11 +24,11 @@ type Theme struct {
 		Hint    color.RGBA
 		InvText color.RGBA
 	}
-	TextSize           unit.Value
+	TextSize              unit.Value
 	checkBoxCheckedIcon   *Icon
 	checkBoxUncheckedIcon *Icon
-	radioCheckedIcon   *Icon
-	radioUncheckedIcon *Icon
+	radioCheckedIcon      *Icon
+	radioUncheckedIcon    *Icon
 }
 
 func NewTheme() *Theme {