Avoided exceptions in admindocs' template detail view.

This is marginally better than crashing when several Django template
engines are configured in a project.

Refs #24125.

django/contrib/admindocs/views.py

@@ -8,7 +8,7 @@ from django.conf import settings
 from django.contrib import admin
 from django.contrib.admin.views.decorators import staff_member_required
 from django.db import models
-from django.core.exceptions import ViewDoesNotExist
+from django.core.exceptions import ImproperlyConfigured, ViewDoesNotExist
 from django.http import Http404
 from django.core import urlresolvers
 from django.contrib.admindocs import utils
@@ -293,13 +293,20 @@ class TemplateDetailView(BaseAdminDocsView):
     def get_context_data(self, **kwargs):
         template = self.kwargs['template']
         templates = []
-        for dir in Engine.get_default().dirs:
-            template_file = os.path.join(dir, template)
+        try:
+            default_engine = Engine.get_default()
+        except ImproperlyConfigured:
+            # Non-trivial TEMPLATES settings aren't supported (#24125).
+            pass
+        else:
+            # This doesn't account for template loaders (#24128).
+            for index, directory in enumerate(default_engine.dirs):
+                template_file = os.path.join(directory, template)
                 templates.append({
                     'file': template_file,
                     'exists': os.path.exists(template_file),
                     'contents': lambda: open(template_file).read() if os.path.exists(template_file) else '',
-                'order': list(Engine.get_default().dirs).index(dir),
+                    'order': index,
                 })
         kwargs.update({
             'name': template,