Fixed #9498 -- Handle a formset correctly when the foreign key is not available (for now).

This case pops up with generic foreign key inlines after [9297]. Added tests
to handle future regressions with generic foreign key inlines in the admin.

Thanks markus and danielr for patches.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9412 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/generic_inline_admin/models.py

@@ -0,0 +1,30 @@
+from django.db import models
+from django.contrib import admin
+from django.contrib.contenttypes import generic
+from django.contrib.contenttypes.models import ContentType
+
+class Episode(models.Model):
+    name = models.CharField(max_length=100)
+
+class Media(models.Model):
+    """
+    Media that can associated to any object.
+    """
+    content_type = models.ForeignKey(ContentType)
+    object_id = models.PositiveIntegerField()
+    content_object = generic.GenericForeignKey()
+    url = models.URLField(verify_exists=False)
+
+    def __unicode__(self):
+        return self.url
+
+class MediaInline(generic.GenericTabularInline):
+    model = Media
+    extra = 1
+    
+class EpisodeAdmin(admin.ModelAdmin):
+    inlines = [
+        MediaInline,
+    ]
+
+admin.site.register(Episode, EpisodeAdmin)