bugfix: don't fetch data on a sold out query

lib/utils/db/query.pm

@@ -70,9 +70,15 @@ sub _get_next {
     my $result = $self->_sth->{$chan}->fetch();
     return $result if ($result);
 
-    # there is no more data to fetch
+    # we come here only if there is no more data to fetch
+
+    # we take care of the db
     $self->_sth->{$chan} = undef;
     $self->_get_dbh($chan)->commit();
+
+    # we remove the query
+    $self->_queries->{$chan} = undef;
+
     return undef;
 }