prevent crashes on filter regexp being too advanced for our database when testing filters (refs #508)

include/functions.php

@@ -2321,7 +2321,20 @@
 
 				$override_order = "updated DESC";
 
-				$filter_query_part = filter_to_sql($filter) . " AND";
+				$filter_query_part = filter_to_sql($filter);
+
+				// Try to check if SQL regexp implementation chokes on a valid regexp
+				$result = db_query($link, "SELECT true FROM ttrss_entries
+					WHERE $filter_query_part LIMIT 1", false);
+
+				$test = db_fetch_result($result, 0, "true");
+
+				if (!$test) {
+					$filter_query_part = "false AND";
+				} else {
+					$filter_query_part .= " AND";
+				}
+
 			} else {
 				$filter_query_part = "";
 			}