fix struct field reference (#578)

Author: felipensp

src/interface_drag_drop.v

@@ -54,7 +54,7 @@ struct Dragger {
 pub mut:
 	typ       string
 	activated bool
-	widget    Draggable = button()
+	widget    &Draggable = button()
 	start_x   f64
 	start_y   f64
 	pos_x     f64
@@ -69,15 +69,15 @@ NB: would like external mechanism only depending on point_inside methods of Widg
 shift key (or other) to activate possible dragging
 */
 
-fn drag_register(d Draggable, e &MouseEvent) bool {
+fn drag_register(d &Draggable, e &MouseEvent) bool {
 	if shift_key(e.mods) {
 		$if drag ? {
 			println('drag ${typeof(w).name}')
 		}
 		mut window := d.get_window()
 		if window.dragger.activated {
 			if d.z_index > window.dragger.widget.z_index {
-				window.dragger.widget = d
+				window.dragger.widget = unsafe { d }
 				window.dragger.start_x = e.x - d.offset_x
 				window.dragger.start_y = e.y - d.offset_y
 				// println('drag: ($e.x, $e.y, ${window.dragger.start_x},${window.dragger.start_y})')
@@ -88,7 +88,7 @@ fn drag_register(d Draggable, e &MouseEvent) bool {
 		} else {
 			window.dragger.activated = true
 			window.mouse.start('blue')
-			window.dragger.widget = d
+			window.dragger.widget = unsafe { d }
 			window.dragger.start_x = e.x - d.offset_x
 			window.dragger.start_y = e.y - d.offset_y
 			// println('drag: ($e.x, $e.y, ${window.dragger.start_x},${window.dragger.start_y})')