Error during update: "field_revision_taxonomyextra" table doesn't exist

On the latest update, #7001, I received the following error:

Failed: PDOException: SQLSTATE[42S02]: Base table or view not found: 1146 Table "field_revision_taxonomyextra" doesn't exist

Although this is not a critical error, it appears to cause the update process to fail. This error could be fixed by first calling db_table_exists() before trying to select the table. Attached is a patch that includes this code.