[extensions-web] extensions: don't cascade drop extensions with their authors.

[Yuri Konotopov <ykonotopov src gnome org>]

commit 7ce9f7a3f0e9f50d209c4861321eace556235705
Author: Yuri Konotopov <ykonotopov gnome org>
Date:   Sat Nov 23 22:49:31 2019 +0400

    extensions: don't cascade drop extensions with their authors.
    
    Closes: https://gitlab.gnome.org/Infrastructure/extensions-web/issues/75

 .../extensions/migrations/0006_auto_20191123_2146.py | 20 ++++++++++++++++++++
 sweettooth/extensions/models.py                      |  2 +-
 2 files changed, 21 insertions(+), 1 deletion(-)
---
diff --git a/sweettooth/extensions/migrations/0006_auto_20191123_2146.py 
b/sweettooth/extensions/migrations/0006_auto_20191123_2146.py
new file mode 100644
index 0000000..69efa78
--- /dev/null
+++ b/sweettooth/extensions/migrations/0006_auto_20191123_2146.py
@@ -0,0 +1,20 @@
+# Generated by Django 2.2.7 on 2019-11-23 21:46
+
+from django.conf import settings
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('extensions', '0005_auto_20190112_1733'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='extension',
+            name='creator',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.PROTECT, 
to=settings.AUTH_USER_MODEL),
+        ),
+    ]
diff --git a/sweettooth/extensions/models.py b/sweettooth/extensions/models.py
index 88857d1..67e283f 100644
--- a/sweettooth/extensions/models.py
+++ b/sweettooth/extensions/models.py
@@ -93,7 +93,7 @@ class Extension(models.Model):
     name = models.CharField(max_length=200)
     uuid = models.CharField(max_length=200, unique=True, db_index=True)
     slug = autoslug.AutoSlugField(populate_from="name")
-    creator = models.ForeignKey(User, db_index=True, on_delete=models.CASCADE)
+    creator = models.ForeignKey(User, db_index=True, on_delete=models.PROTECT)
     description = models.TextField(blank=True)
     url = models.URLField(blank=True)
     created = models.DateTimeField(auto_now_add=True)