Fix sporadic crash on home screen

[cewert]

Comes from roku crashlog:

Invalid value for left-side of expression. (runtime error &he4) in pkg:/components/home/HomeItem.brs(34) Backtrace: #0  Function itemcontentchanged() As Void    file/line: pkg:/components/home/HomeItem.brs(35) Local Variables: global           Interface:ifGlobal m                roAssociativeArray refcnt=2 count:2 itemdata         <uninitialized> playedindicatorleftposition <uninitialized> extraprefix      <uninitialized> textextra        <uninitialized>

Which points to line 39 in the bs file: m.unplayedCount.visible = false

Changes

• Ensure node is valid before using

Issues

Ref #1662