Do not allow more than 20 terms in search queries

Specifying a huge number of search terms currently results in complex
SQL queries. In practice, queries with more than 20 terms are rarely
needed. Ignore everything apart from the first 20 keywords to prevent
from potential abuse.
Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>

web/lib/pkgfuncs.inc.php

@@ -601,10 +601,21 @@ function pkg_search_page($SID="") {
 		}
 		else {
 			/* Search by name and description (default). */
+			$count = 0;
+
 			foreach (str_getcsv($_GET['K'], ' ') as $term) {
+				if ($term == "") {
+					continue;
+				}
+
 				$term = "%" . addcslashes($term, '%_') . "%";
 				$q_where .= "AND (Packages.Name LIKE " . $dbh->quote($term) . " OR ";
 				$q_where .= "Description LIKE " . $dbh->quote($term) . ") ";
+
+				$count++;
+				if ($count >= 20) {
+					break;
+				}
 			}
 		}
 	}