Force tardiness to be positive

Closes #141

aleksis/apps/alsijil/migrations/0011_tardiness_positive.py

+# Generated by Django 3.1.6 on 2021-02-26 17:45
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('alsijil', '0010_events_extra_lessons'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='personalnote',
+            name='late',
+            field=models.PositiveSmallIntegerField(default=0),
+        ),
+    ]

aleksis/apps/alsijil/models.py

@@ -193,7 +193,7 @@ class PersonalNote(RegisterObjectRelatedMixin, ExtensibleModel):
     )
 
     absent = models.BooleanField(default=False)
-    late = models.IntegerField(default=0)
+    late = models.PositiveSmallIntegerField(default=0)
     excused = models.BooleanField(default=False)
     excuse_type = models.ForeignKey(
         ExcuseType, on_delete=models.SET_NULL, null=True, blank=True, verbose_name=_("Excuse type"),