misc: only expose existing templates in styles demo page (#22439)

combo/public/views.py

@@ -29,6 +29,7 @@ from django.http import (Http404, HttpResponse, HttpResponseRedirect,
         HttpResponsePermanentRedirect)
 from django.shortcuts import render, resolve_url
 from django.template import engines
+from django.template.loader import get_template, TemplateDoesNotExist
 from django.utils import lorem_ipsum, timezone
 from django.views.decorators.csrf import csrf_exempt
 
@@ -275,6 +276,11 @@ class StyleDemoPage(object):
                 cell = TextCell(page=self.page, placeholder=placeholder.key, order=1)
                 options_html = []
                 for template_key, template_dict in settings.COMBO_PUBLIC_TEMPLATES.items():
+                    try:
+                        get_template(template_dict.get('template'))
+                    except TemplateDoesNotExist:
+                        # don't propose templates that do not exist
+                        continue
                     attr = 'value="%s"' % template_key
                     if template_key == self.page.template_name:
                         attr += ' selected="selected"'