fix: an opened file's password becomes the document's only once the file is loaded

Declining to replace the current document, or an import that throws, left
the foreign password on the document that stayed open, and an unprotected
file kept the previous document's password. Both now travel with the load.

src/App.svelte

@@ -654,7 +654,7 @@
   }
 
   // Ask until the password fits or the user gives up; null means give up.
-  async function unprotect(bytes: Uint8Array): Promise<Uint8Array | null> {
+  async function unprotect(bytes: Uint8Array): Promise<{ bytes: Uint8Array; password: string } | null> {
     for (;;) {
       const password = await new Promise<string | null>((resolve) => {
         askResolve = resolve;
@@ -663,9 +663,8 @@
       if (password === null) return null;
       try {
         const plain = await decryptPackage(bytes, password);
-        docPassword = password;
         passwordWrong = false;
-        return plain;
+        return { bytes: plain, password };
       } catch (err) {
         if ((err as Error)?.message !== WRONG_PASSWORD) throw err;
         passwordWrong = true;
@@ -677,10 +676,11 @@
     if (!editor) return;
     try {
       // Before anything reads the archive: an encrypted file is not one yet.
+      let password: string | null = null;
       if (isProtected(bytes)) {
         const opened = await unprotect(bytes);
         if (!opened) return;
-        bytes = opened;
+        ({ bytes, password } = opened);
       }
       const name = sourceName?.toLowerCase() ?? '';
       let isDocx = name.endsWith('.docx') || name.endsWith('.dotx');
@@ -761,6 +761,9 @@
       };
       fileHandle = isTemplate ? null : handle;
       documentFormat = isDocx ? 'docx' : 'odt';
+      // The file's password belongs to the document once it is actually the open one,
+      // and an unprotected file drops the previous document's.
+      docPassword = password;
       if (sourceName) recentFiles = await rememberRecentFile(sourceName, isTemplate ? null : handle);
 
       // Warn about fonts the document uses but the browser can't render, so text