File cache changes take 2, a=chris

diff --git a/src/library/FileCache.php b/src/library/FileCache.php
index 78848f808..e7cc5d7ce 100644
--- a/src/library/FileCache.php
+++ b/src/library/FileCache.php
@@ -122,12 +122,12 @@ class FileCache
                 than time, but we store time anyway.
                 */
         }
+        $cache_file = "$checksum_dir/".webencode($key);
         if (!file_exists($cache_file)) {
             $data['count']++;
         }
         file_put_contents("$checksum_dir/last_expired.txt",
             serialize($data));
-        $cache_file = "$checksum_dir/".webencode($key);
         file_put_contents($cache_file, serialize($value));
     }
     /**