private_taxonomy_unwrap_conditions() can't handle conditions not specifying a table

private_taxonomy_unwrap_conditions() checks every condition to see if vid is a field on which there is a condition. When vid is used without specifying a table, the call to explode() generates a warning because there is no "." in the condition. For example:

$q = db_select("taxonomy_term_data")->fields('taxonomy_term_data', array('tid'))->addTag("term_access");
$q->condition("vid", 2);
$q->execute();

results in a warning because vid didn't specify its table.