addresses #648

dereferencing value in debug statement that could be NULL
this fixes it.

git-svn-id: file:///svn/mysql/tokudb-engine/src@3276 c7de825b-a66e-492c-adef-691d508d4ae1

storage/tokudb/ha_tokudb.cc

@@ -1735,7 +1735,7 @@ int ha_tokudb::read_row(int error, uchar * buf, uint keynr, DBT * row, DBT * fou
         row = &current_row;
     }
     unpack_row(buf, row);
-    DBUG_DUMP("read row key", (uchar *) found_key->data, found_key->size);
+    if (found_key) { DBUG_DUMP("read row key", (uchar *) found_key->data, found_key->size); }
     TOKUDB_DBUG_RETURN(0);
 }