Proxito: always check 404/index.hmtml

With the introduction of `build.commands` we cannot use
`version.documentation_type` anymore since those versions will be `generic` and
we can't skip checking for this file location.

Note this commit may add and extra call to S3 API for all the 404 pages where
our regular Maze will be shown. However, it removes 2 databsae calls from all
the 404 requests.

We could only add this extra check on S3 for
`version.documentation_type='generic'`, but that would make the code a little
more complex and we won't be removing these 2 db queries.

Reference: readthedocs/sphinx-notfound-page#215 (comment)

Author: humitos

readthedocs/proxito/views/serve.py

@@ -19,7 +19,6 @@
 from readthedocs.core.resolver import resolve_path
 from readthedocs.core.utils.extend import SettingsOverrideObject
 from readthedocs.projects import constants
-from readthedocs.projects.constants import SPHINX_HTMLDIR
 from readthedocs.projects.models import Feature
 from readthedocs.projects.templatetags.projects_tags import sort_version_aware
 from readthedocs.redirects.exceptions import InfiniteRedirectException
@@ -347,24 +346,14 @@ def get(self, request, proxito_path, template_name='404.html'):
         # If that doesn't work, attempt to serve the 404 of the current version (version_slug)
         # Secondly, try to serve the 404 page for the default version
         # (project.get_default_version())
-        version = (
-            Version.objects.filter(project=final_project, slug=version_slug)
-            .only("documentation_type")
-            .first()
-        )
         versions = []
-        if version:
-            versions.append((version.slug, version.documentation_type))
+        if Version.objects.filter(project=final_project, slug=version_slug).exists():
+            versions.append(version_slug)
         default_version_slug = final_project.get_default_version()
         if default_version_slug != version_slug:
-            default_version_doc_type = (
-                Version.objects.filter(project=final_project, slug=default_version_slug)
-                .values_list('documentation_type', flat=True)
-                .first()
-            )
-            versions.append((default_version_slug, default_version_doc_type))
+            versions.append(default_version_slug)
 
-        for version_slug_404, doc_type_404 in versions:
+        for version_slug_404 in versions:
             if not self.allowed_user(request, final_project, version_slug_404):
                 continue
 
@@ -374,11 +363,7 @@ def get(self, request, proxito_path, template_name='404.html'):
                 include_file=False,
                 version_type=self.version_type,
             )
-            tryfiles = ['404.html']
-            # SPHINX_HTMLDIR is the only builder
-            # that could output a 404/index.html file.
-            if doc_type_404 == SPHINX_HTMLDIR:
-                tryfiles.append('404/index.html')
+            tryfiles = ["404.html", "404/index.html"]
             for tryfile in tryfiles:
                 storage_filename_path = build_media_storage.join(storage_root_path, tryfile)
                 if build_media_storage.exists(storage_filename_path):