Avoid unnecessary /nav API call

package.json

@@ -1,6 +1,6 @@
 {
     "name": "fwdekker.com",
-    "version": "0.39.16",
+    "version": "0.39.17",
     "description": "The source code of [my personal website](https://fwdekker.com/).",
     "author": "Felix W. Dekker",
     "browser": "dist/bundle.js",

src/main/js/Main.ts

@@ -60,6 +60,7 @@ addOnLoad(() => {
  * Initializes the application.
  */
 addOnLoad(async () => {
+    if (!Persistence.hasFileSystem())
         await FileSystem.loadNavApi();
 
     window.terminal = new Terminal(

src/main/js/Persistence.ts

@@ -26,6 +26,15 @@ export class Persistence {
     /// Long-term storage
     ///
 
+    /**
+     * Returns true if and only if a file system is stored in the persistent storage.
+     *
+     * @return true if and only if a file system is stored in the persistent storage
+     */
+    static hasFileSystem(): boolean {
+        return localStorage.getItem("//files") !== null;
+    }
+
     /**
      * Deserializes a file system from persistent storage, or returns the default file system if the deserialization
      * failed.