BListView: Contain scroll within scroll area horizontally

... but extending vertically above and below the list view.

https://www.haiku-os.org/legacy-docs/bebook/BListView_Overview.html

"BListView provides an autoscroll feature: There's an invisible area
about 25 pixels high both above and below the list view; if the user
clicks inside the list view and then drags into this autoscroll area,
the contents of the list will scroll in the direction of the mouse."

Instead of 25px scroll vertically without limit because scrolling
speeds up as you move the mouse cursor further away.

Change-Id: I52296beb2b0173fc5c909255163e8725e99c2b6c
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7244
Reviewed-by: waddlesplash <[email protected]>
Tested-by: Commit checker robot <[email protected]>

src/kits/interface/ListView.cpp

@@ -742,6 +742,10 @@ BListView::MouseMoved(BPoint where, uint32 code, const BMessage* dragMessage)
 	if (buttons == 0 || index == -1)
 		return BView::MouseMoved(where, code, dragMessage);
 
+	// don't scroll if mouse is left or right of the view
+	if (where.x < Bounds().left || where.x > Bounds().right)
+		return BView::MouseMoved(where, code, dragMessage);
+
 	// scroll to item under mouse while button is pressed
 	ScrollTo(index);