Disable a LGTM warning, again (PR 13787 follow-up)

Apparently I didn't put one of the disable comments on the *correct* line, since I didn't read the instructions carefully enough, so let's try again.

Note that, most unfortunately, disabling of warnings isn't applied until *after* a patch has been merged.

Author: Snuffleupagus

src/core/file_spec.js

@@ -66,8 +66,8 @@ class FileSpec {
   get filename() {
     if (!this._filename && this.root) {
       const filename = pickPlatformItem(this.root) || "unnamed";
-      this._filename = stringToPDFString(filename)
-        .replace(/\\\\/g, "\\") // lgtm [js/double-escaping]
+      this._filename = stringToPDFString(filename) // lgtm [js/double-escaping]
+        .replace(/\\\\/g, "\\")
         .replace(/\\\//g, "/")
         .replace(/\\/g, "/");
     }