Fix options menu scrolling incorrectly when there is no cursor on the menu and scrolling keys are being pressed.

[Bitl]

I noticed recently that after implementing commit 53869ad into my project, that the options menu exhibits the following behavior:

• If you remove your cursor from the menu and press the up or down arrows or controller buttons, it will scroll down to a certain point and reset itself.

I noticed that it doesn't do this in Portal or any other Valve games that use gamepadui, so I whipped up a patch that does the following:

1. when the mouse is hovering over the panel, it will enable the current solution and prevent the menu from scrolling incorrectly with the mouse.
2. when the mouse is NOT hovering over the panel, it will enable the original code from the initial commit of this repo (the code shipped with Portal and HL2's GamepadUI)