[layouts] Fix export to pdf reports a print error instead of a file e…

…rror on inaccessible file names

(cherry-picked from 5498204)

src/core/layout/qgslayoutexporter.cpp

@@ -486,7 +486,7 @@ QgsLayoutExporter::ExportResult QgsLayoutExporter::exportToPdf( const QString &f
   if ( !p.begin( &printer ) )
   {
     //error beginning print
-    return PrintError;
+    return FileError;
   }
 
   ExportResult result = printPrivate( printer, p, false, settings.dpi, settings.rasterizeWholeImage );