Updated regexp in assets::buildCss() to fix issue where it matched …

…a trailing quote, and streamlined how it handles inline data URI's.

Fixed bugs where `realpath()` cannot handle URL's with querystrings or hashbangs, it now just uses the path component.
Updated `config::__construct()` to handled the return value of `overview::draw()` as a string or null.

assets.php

@@ -232,10 +232,10 @@ public static function buildCss(array $files, string $target, ?array $minify = n
 		// get the CSS documents and rewrite the URL's
 		$css = '';
 		foreach ($files AS $item) {
-			if (($file = \file_get_contents($dir.$item)) !== false) {
-				$css .= \preg_replace_callback('/url\\([\'"]?+(?!data:)([^\\)]++)[\'"]?\\)/i', function (array $match) use ($item) {
+			if (($file = \file_get_contents($item)) !== false) {
+				$css .= \preg_replace_callback('/url\\([\'"]?+([^\\)"\':]++)[\'"]?\\)/i', function (array $match) use ($item) {
 					\chdir(\dirname($item));
-					$path = \realpath($match[1]);
+					$path = \realpath(\dirname($match[1])).'/'.\basename($match[1]);
 					return 'url('.\str_replace('\\', '/', \substr($path, \strlen($_SERVER['DOCUMENT_ROOT']))).')';
 				}, $file);
 			}

config.php

@@ -536,7 +536,7 @@ class config extends packages {
 	public function __construct() {
 
 		// render the overview
-		$this->options['overview']['html'] = function () : string {
+		$this->options['overview']['html'] = function () : ?string {
 			$obj = new overview();
 			return $obj->draw();
 		};