Restrict valid page names

plugs/core/page.ts

@@ -139,7 +139,7 @@ export async function renamePage(cmdDef: any) {
 
   if (!isValidPageName(newName)) {
     return editor.flashNotification(
-      "Invalid page name: page names cannot end with a file extension",
+      "Invalid page name: page names cannot end with a file extension nor start with a '.'",
       "error",
     );
   }

plugs/markdown/markdown_render.ts

@@ -394,8 +394,8 @@ export function renderMarkdownToHtml(
         t.attrs!.src = options.translateUrls!(t.attrs!.src!);
       }
 
-      if (t.name === "a") {
-        t.attrs!.href = options.translateUrls!(t.attrs!.href!);
+      if (t.name === "a" && t.attrs!.href) {
+        t.attrs!.href = options.translateUrls!(t.attrs!.href);
       }
     });
   }