TripCard: don't show footer if no notes

On trips with no notes/additions, an empty <View> was being rendered (causing a 10px gap due to padding)
If there were no notes, `timelineNotesMap[trip._id.$oid]` would be `undefined`, which does not equal 0.
We should only show notes if it is defined AND the length is not 0, so we can just say `timelineNotesMap[trip._id.$oid]?.length`.

www/js/diary/cards/TripCard.tsx

@@ -92,7 +92,7 @@ const TripCard = ({ trip }: Props) => {
           }
         </View>
       </View>
-      {timelineNotesMap[trip._id.$oid]?.length != 0 &&
+      {timelineNotesMap[trip._id.$oid]?.length &&
         <View style={cardStyles.cardFooter}>
           <AddedNotesList timelineEntry={trip} additionEntries={timelineNotesMap[trip._id.$oid]} />
         </View>