Ignore io errors when deleting unit

The index might be non existing and we do not want to fail on it.

Fixes rb#498, rb#499
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/search.py

@@ -303,7 +303,10 @@ def more_like(pk, source, top=5):
 
 def clean_search_unit(pk, lang):
     """Cleanups search index on unit deletion."""
-    index = get_target_index(lang)
-    index.writer().delete_by_term('pk', pk)
-    index = get_source_index()
-    index.writer().delete_by_term('pk', pk)
+    try:
+        index = get_target_index(lang)
+        index.writer().delete_by_term('pk', pk)
+        index = get_source_index()
+        index.writer().delete_by_term('pk', pk)
+    except IOError:
+        return