Model uid validator: fix off-by-1 error with the uid.

256bit is actually 43 base64 chars, not 44.

django_etesync/migrations/0016_auto_20200226_1446.py

@@ -0,0 +1,29 @@
+# Generated by Django 3.0.3 on 2020-02-26 14:46
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('django_etesync', '0015_auto_20200226_1349'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='collection',
+            name='uid',
+            field=models.CharField(db_index=True, max_length=44, validators=[django.core.validators.RegexValidator(message='Not a valid UID. Expected a 256bit base64url.', regex='[a-zA-Z0-9\\-_=]{43}')]),
+        ),
+        migrations.AlterField(
+            model_name='collectionitem',
+            name='uid',
+            field=models.CharField(db_index=True, max_length=44, validators=[django.core.validators.RegexValidator(message='Not a valid UID. Expected a 256bit base64url.', regex='[a-zA-Z0-9\\-_=]{43}')]),
+        ),
+        migrations.AlterField(
+            model_name='collectionitemchunk',
+            name='uid',
+            field=models.CharField(db_index=True, max_length=44, validators=[django.core.validators.RegexValidator(message='Not a valid UID. Expected a 256bit base64url.', regex='[a-zA-Z0-9\\-_=]{43}')]),
+        ),
+    ]

django_etesync/models.py

@@ -20,7 +20,7 @@ from django.core.validators import RegexValidator
 from django.utils.functional import cached_property
 
 
-UidValidator = RegexValidator(regex=r'[a-zA-Z0-9\-_=]{44}', message='Not a valid UID. Expected a 256bit base64url.')
+UidValidator = RegexValidator(regex=r'[a-zA-Z0-9\-_=]{43}', message='Not a valid UID. Expected a 256bit base64url.')
 
 
 class Collection(models.Model):