Trim leading whitespace and brackets before detecting query type

[johnbillion]

The filter_mysql_query() method adds a # Trace ID: comment to the end of non-SELECT queries to aid debugging slow queries. Some queries include other characters before the SELECT clause and therefore the trace ID comment still gets added to these.

Example query from MultilingualPress:

(SELECT DISTINCT site_1 AS site_id
FROM wp_mlp_site_relations
WHERE site_2 = 6)
UNION (SELECT DISTINCT site_2
FROM wp_mlp_site_relations
WHERE site_1 = 6)
ORDER BY site_id ASC # Trace ID: 1-63078aa8-43fb2162947f5d5e915ab956

The Query Monitor plugin strips more than just whitespace from the start of the SQL before determining its type, so the same can be done here.

Ref: https://github.com/johnbillion/query-monitor/blob/9a7600f3990710807c300079ad286c445f69fd83/classes/Util.php#L500-L502

[shadyvb]

LGTM!