Fix new Uri() for relative URLs with param colon

Fixes #6331

src/Http/Environment.php

@@ -602,13 +602,7 @@ protected function detectPortInHost(string|null $host = null): array
 	 */
 	protected function detectRequestUri(string|null $requestUri = null): Uri
 	{
-		// make sure the URL parser works properly when there's a
-		// colon in the request URI but the URI is relative
-		if (Url::isAbsolute($requestUri) === false) {
-			$requestUri = 'https://getkirby.com' . $requestUri;
-		}
-
-		$uri = new Uri($requestUri);
+		$uri = new Uri($requestUri ?? '');
 
 		// create the URI object as a combination of base uri parts
 		// and the parts from REQUEST_URI

src/Http/Uri.php

@@ -88,7 +88,16 @@ class Uri
 	public function __construct(array|string $props = [], array $inject = [])
 	{
 		if (is_string($props) === true) {
-			$props = parse_url($props);
+			// make sure the URL parser works properly when there's a
+			// colon in the string but the string is a relative URL
+			if (Url::isAbsolute($props) === false) {
+				$props = 'https://getkirby.com/' . $props;
+				$props = parse_url($props);
+				unset($props['scheme'], $props['host']);
+			} else {
+				$props = parse_url($props);
+			}
+
 			$props['username'] = $props['user'] ?? null;
 			$props['password'] = $props['pass'] ?? null;