Issue #3594274: Restore the file input on upload error so the user can retry

Ethan Teaguerequested to merge
issue/s3fs_cors-3594274:3594274-restore-file-input-on-error into 8.x-1.x

createProgressBar() hides the file input (display:none) before the upload promise chain runs. On any failure (oversize rejection, extension mismatch, S3 error, save error) showError() runs but nothing restores the input, so the user is left with only an error and no way to pick another file. This restores fileInput.style.display in showError so the input reappears on error. On success the widget AJAX re-renders, so it's a no-op there.

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