PDF: fix the encoding for the file name of attachments

A file specification in PDF is a string (§3.10.1 of the PDF 1.6 spec).
As such, it needs to be properly encoded. Right now the code was
doing a naive conversion to latin1 (which was lossy), and was not
considering things like round parenthesis which need to be properly
escaped. Just use printString instead.

This work has been kindly sponsored by the QGIS project
(https://qgis.org/).

Change-Id: Icdcf8b553955d31fe2bc430dea54bb6e68221fc7
Pick-to: 6.7 6.5
Reviewed-by: Albert Astals Cid <aacid@kde.org>

src/gui/painting/qpdf.cpp

@@ -1911,7 +1911,8 @@ void QPdfEnginePrivate::writeAttachmentRoot()
 
         attachments.push_back(addXrefEntry(-1));
         xprintf("<<\n"
-                "/F (%s)", attachment.fileName.toLatin1().constData());
+                "/F ");
+        printString(attachment.fileName);
 
         xprintf("\n/EF <</F %d 0 R>>\n"
                 "/Type/Filespec\n"