Fix - store PDF file with images

Raw string has special symbols which does not work directly with JS Blob object.
One need to convert string to ArrayBuffer before providing it to Blob

Author: linev

modules/gui/utils.mjs

@@ -564,7 +564,12 @@ async function saveFile(filename, content) {
    if ((content.length > 1e6) && (contentType === 'application/pdf')) {
       // large PDF files do not work in the browser with plain base64 coding
       const bindata = getBinFileContent(content),
-            blob = new Blob([bindata], { type: contentType });
+            len = bindata.length,
+            buffer = new ArrayBuffer(len),
+            view = new DataView(buffer, 0, len);
+      for (let i = 0; i < len; ++i)
+         view.setUint8(i, bindata.charCodeAt(i));
+      const blob = new Blob([buffer], { type: contentType });
       fileURL = URL.createObjectURL(blob);
       a.href = fileURL;
    } else