added a lock on a critical path when regenerating pages. this should allow all images to load correctly

comic/migrations/0020_alter_directory_options.py

@@ -0,0 +1,17 @@
+# Generated by Django 3.2 on 2021-04-08 15:14
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('comic', '0019_auto_20190730_1846'),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name='directory',
+            options={'ordering': ['name']},
+        ),
+    ]