better index manager error checking, a=chris

diff --git a/src/library/IndexManager.php b/src/library/IndexManager.php
index e8e10f33a..761f78374 100644
--- a/src/library/IndexManager.php
+++ b/src/library/IndexManager.php
@@ -235,9 +235,15 @@ class IndexManager implements CrawlConstants
                         $feed_info[1], $feed_info[2], $feed_info[3]];
                 }
             }
-            list($total, $info) =
+            $pre_info =
                 $index->dictionary->getWordInfo($hash, true, $shift, $mask,
                 $threshold, $start_generation, $num_distinct_generations, true);
+            if (isset($pre_info[1])) {
+                list($total, $info) = $pre_info;
+            } else {
+                $total = 0;
+                $info = [];
+            }
             if (isset($tmp[-1][3])) {
                 $total += $tmp[-1][3];
                 $info = $tmp + $info;