Import polyline rail tool patch v10b

http://www.tt-forums.net/viewtopic.php?f=33&t=57080

src/window.cpp

@@ -2796,7 +2796,7 @@ static void MouseLoop(MouseClick click, int mousewheel)
 			case MC_DOUBLE_LEFT:
 			case MC_LEFT:
 				DEBUG(misc, 2, "Cursor: 0x%X (%d)", _cursor.sprite, _cursor.sprite);
-				if (!HandleViewportClicked(vp, x, y) &&
+				if (!HandleViewportClicked(vp, x, y, click == MC_DOUBLE_LEFT) &&
 						!(w->flags & WF_DISABLE_VP_SCROLL) &&
 						_settings_client.gui.left_mouse_btn_scrolling) {
 					_scrolling_viewport = true;