[damned-lies] Prevent crash in building docs

[Claude Paroz <claudep src gnome org>]

commit d81f9449bb655a737b742b07a2ca54c8c0588571
Author: Claude Paroz <claude 2xlibre net>
Date:   Sat Jan 19 14:55:32 2019 +0100

    Prevent crash in building docs

 vertimus/views.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/vertimus/views.py b/vertimus/views.py
index 7685c2af..b821ac8b 100644
--- a/vertimus/views.py
+++ b/vertimus/views.py
@@ -374,7 +374,7 @@ class BuildTranslatedDocsView(PoFileActionBase):
                     'program': 'yelp-build', 'err': result.stderr.decode()
                 }
 
-            if not index_html.exists():
+            if not index_html.exists() and os.path.isfile(build_ref[0]):
                 # Create an index.html symlink to the base html doc if needed
                 try:
                     doc = parse(build_ref[0])