tdf#94739 use GetScanlineSize instead of calculating it

We calculate the scanline size wrongly when writing a PDF so the
image is not exported correctly. BitmapAccess already has a method
to determine the scanline size so use that instead.

Change-Id: Icccba8f26c5e0fd4bd4c37bba7c5a7fe8d0094bd
(cherry picked from commit 82e0c38e)
Signed-off-by: Michael Meeks <michael.meeks@collabora.com>
Reviewed-on: https://gerrit.libreoffice.org/20595Tested-by: Jenkins <ci@libreoffice.org>

vcl/source/gdi/pdfwriter_impl.cxx

@@ -11426,7 +11426,7 @@ bool PDFWriterImpl::writeBitmapObject( BitmapEmit& rObject, bool bMask )
         beginCompression();
         if( ! bTrueColor || pAccess->GetScanlineFormat() == BMP_FORMAT_24BIT_TC_RGB )
         {
-            const int nScanLineBytes = 1 + ( pAccess->GetBitCount() * ( pAccess->Width() - 1 ) / 8U );
+            const int nScanLineBytes = pAccess->GetScanlineSize();
 
             for( int i = 0; i < pAccess->Height(); i++ )
             {