fix: guard scrollSelectedIntoView against viewport scroll

[shaah1d]

Problem

When <Command /> is mounted off-screen (below the fold), it internally calls Element.scrollIntoView() on the selected item at mount time. If the <CommandList> has no overflow/scroll (i.e. it isn't tall enough to scroll), the browser escalates the scrollIntoView call to the viewport, causing the entire page to jump down to where the component is mounted.

Fix

Added an early return in scrollSelectedIntoView() when the list has nothing to scroll (scrollHeight <= clientHeight). This prevents both the item and group heading scrollIntoView calls from firing when the list isn't scrollable, stopping the viewport from being affected.

##Testing
Tested by placing below a "150vh" spacer and checking if it auto scrolls or not when refreshed.

Closes #405