home: make thumb visible if provider is found

Make the thumb visible if a popup provider is found later.

Fixes an issue where the fast scroll thumb would only be visible
sometimes in the home view.

app/src/main/java/org/oxycblt/auxio/home/fastscroll/FastScrollRecyclerView.kt

@@ -212,6 +212,7 @@ constructor(context: Context, attrs: AttributeSet? = null, @AttrRes defStyleAttr
         val popupText: String
         val provider = popupProvider
         if (firstPos != NO_POSITION && provider != null) {
+            popupView.isInvisible = false
             // Get the popup text. If there is none, we default to "?".
             popupText = provider.getPopup(firstPos) ?: "?"
         } else {