pdf: Image: error: RBPDF error: Image filename is empty.

[naitoh]

This problem is https://www.redmine.org/issues/28125#note-2

pdf: Image: error: RBPDF error: Image filename is empty.

Although I could not reproduce it, I corrected the processing which is considered as a cause.
I was closing the temporary file to save the file with RBPDF.
Therefore, there was a possibility that files were deleted when GC occurred.

Fixed to save file contents with fsync().

[naitoh]

fixed fa1506f