Fix and improve absences query for coursebook

aleksis/apps/alsijil/frontend/components/coursebook/Coursebook.vue

@@ -192,7 +192,7 @@ export default {
         dateStart: this.dateStart,
         dateEnd: this.dateEnd,
         incomplete: !!this.incomplete,
-        absencesExist: !!this.absencesExist,
+        absencesExist: !!this.absencesExist && this.pageType === "absences",
       };
     },
     filters: {

aleksis/apps/alsijil/models.py

@@ -567,8 +567,8 @@ class Documentation(CalendarEvent):
                 if (incomplete and doc.topic) or (
                     absences_exist
                     and (
-                        not doc.participations.exists
-                        or not doc.participations.filter(absence_reason__isnull=False).exists()
+                        not doc.participations.all()
+                        or not [d for d in doc.participations.all() if d.absence_reason]
                     )
                 ):
                     continue