add 404 handler

modules/view.xql

@@ -54,7 +54,12 @@ let $project := $project-path[1]
 let $resource := $project-path[last()]
 let $doc-path := $config:projects-dir || $project || config:get("template") || $resource
 
-let $content := doc( $doc-path )
+let $content :=
+    if( doc-available($doc-path)) then doc( $doc-path )
+    else
+        (doc($config:projects-dir || $project || config:get("template") || "/error.html"),
+        response:set-status-code( 404 )
+        )
 
 return
     templates:apply($content, $lookup, (), $config)