fix filter testing on mysql

include/functions.php

@@ -2281,11 +2281,11 @@
 				$filter_query_part = filter_to_sql($link, $filter, $owner_uid);
 
 				// Try to check if SQL regexp implementation chokes on a valid regexp
-				$result = db_query($link, "SELECT true AS true FROM ttrss_entries,
+				$result = db_query($link, "SELECT true AS true_val FROM ttrss_entries,
 					ttrss_user_entries, ttrss_feeds, ttrss_feed_categories
 					WHERE $filter_query_part LIMIT 1", false);
 
-				$test = db_fetch_result($result, 0, "true");
+				$test = db_fetch_result($result, 0, "true_val");
 
 				if (!$test) {
 					$filter_query_part = "false AND";