A fix (bug #8799: Killed filesorts can fail inited==RND assertion in ha_rnd_end).

sql/filesort.cc:
  A fix (bug #8799: Killed filesorts can fail inited==RND assertion in ha_rnd_end).              
  Should call ha_rnd_end() only if ha_rnd_init() was called.

sql/filesort.cc

@@ -452,8 +452,11 @@ static ha_rows find_all_keys(SORTPARAM *param, SQL_SELECT *select,
     if (*killed)
     {
       DBUG_PRINT("info",("Sort killed by user"));
+      if (!indexfile && !quick_select)
+      {
         (void) file->extra(HA_EXTRA_NO_CACHE);
         file->ha_rnd_end();
+      }
       DBUG_RETURN(HA_POS_ERROR);		/* purecov: inspected */
     }
     if (error == 0)