Add Content-Type response header for error responses (#1)

Reviewed-on: https://codeberg.org/vlw/blobber/pulls/1
Co-authored-by: Victor Westerlund <victor.vesterlund@gmail.com>
Co-committed-by: Victor Westerlund <victor.vesterlund@gmail.com>

src/Router.php

@@ -46,9 +46,11 @@
 
 			// Return HTML page if supported by client
 			if ($_SERVER["HTTP_ACCEPT"] === "*/*" || strpos($_SERVER["HTTP_ACCEPT"] ?? "", "text/html") !== false) {
+				header("Content-Type: text/html", true);
 				die(sprintf(file_get_contents(__DIR__ . "/error.html"), $error->value, $error->name));
 			}
 
+			header("Content-Type: text/plain", true);
 			die($error->name);
 		}