webpositive: force download window on screen.

* When Download window is initially shown, it is correctly
  fully onscreen; however, adding a download resizes the
  window such that it becomes partially offscreen. Now,
  when the frame is resized, reposition the window onscreen
  again.

Fixes #12704

src/apps/webpositive/DownloadWindow.cpp

@@ -223,6 +223,13 @@ DownloadWindow::DispatchMessage(BMessage* message, BHandler* target)
 }
 
 
+void
+DownloadWindow::FrameResized(float newWidth, float newHeight)
+{
+	MoveOnScreen(B_DO_NOT_RESIZE_TO_FIT | B_MOVE_IF_PARTIALLY_OFFSCREEN);
+}
+
+
 void
 DownloadWindow::MessageReceived(BMessage* message)
 {

src/apps/webpositive/DownloadWindow.h

@@ -26,6 +26,7 @@ public:
 
 	virtual	void				DispatchMessage(BMessage* message,
 									BHandler* target);
+	virtual void				FrameResized(float newWidth, float newHeight);
 	virtual	void				MessageReceived(BMessage* message);
 	virtual	bool				QuitRequested();