🐛 Matching any substitution on empty lessons

If a timetable lesson is empty (eg. has no teacher),
just matching any lesson to it is not intended behaviour,
like it is the other way around.

src/components/timetable-list.vue

@@ -24,7 +24,7 @@ const linkedTimetable = computed(() => {
           return (
             entry.lesson == index + 1 &&
             entryDay == props.date.getTime() &&
-            (entry.teacher == e.teacher || !entry.teacher || !e.teacher)
+            (entry.teacher == e.teacher || !entry.teacher)
           );
         },
       );