Don't crash metadata API route if timestamp file is not ready

flatisfy/web/routes/api.py

@@ -520,15 +520,20 @@ def metadata_v1(config):
         # CORS
         return {}
 
+    try:
+        last_update = None
         try:
             ts_file = os.path.join(
                 config['data_directory'],
                 'timestamp'
             )
-        ts = os.path.getmtime(ts_file)
+            last_update = os.path.getmtime(ts_file)
+        except OSError:
+            pass
+
         return {
             'data': {
-                'last_update': ts
+                'last_update': last_update
             }
         }
     except Exception as exc:  # pylint: disable= broad-except