Make prop calls not fail when there is no function

src/lib/AddStreamDialog.svelte

@@ -8,7 +8,7 @@
     let streamId = $state("doggoat");
 </script>
 
-<Dialog close={() => close()}>
+<Dialog close={() => close?.()}>
     <div class="add-stream-dialog">
         {#if step === 0}
             <div class="step-0">
@@ -46,7 +46,7 @@
                 >
                 <button
                     onclick={() => {
-                        add({ type, streamId });
+                        add?.({ type, streamId });
                         step = 0;
                     }}>Add</button
                 >

src/lib/ManageStreamDialog.svelte

@@ -4,7 +4,7 @@
     let { streams = $bindable(null), close } = $props();
 </script>
 
-<Dialog close={() => close()}>
+<Dialog close={() => close?.()}>
     <pre>
       {JSON.stringify(streams)}
     </pre>