Demos: Fix a bunch of incorrect use of GUI::PaintEvent::rect()

A bunch of programs were using the paint event rect as the rect
to draw into. Since the event rect could be any invalidated part
of the widget, we need to be passing the full Widget::rect().

Userland/Demos/Fire/Fire.cpp

@@ -118,9 +118,7 @@ void Fire::paint_event(GUI::PaintEvent& event)
 
     GUI::Painter painter(*this);
     painter.add_clip_rect(event.rect());
-
-    /* Blit it! */
-    painter.draw_scaled_bitmap(event.rect(), *bitmap, bitmap->rect());
+    painter.draw_scaled_bitmap(rect(), *bitmap, bitmap->rect());
 
     timeAvg += timer.elapsed();
     cycles++;