Fix unconditional seek in sanedlg

I fixed my previous mistake of keeping that
   xTransporter->getStream().Seek( STREAM_SEEK_TO_END );
in live code by wrapping it under OSL_DEBUG_LEVEL > 0 .

Change-Id: I3f3bd3308e90610ab3d14f112e4da8bf46ecd25c
Reviewed-on: https://gerrit.libreoffice.org/24188Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>

extensions/source/scanner/sanedlg.cxx

@@ -905,8 +905,10 @@ void SaneDlg::AcquirePreview()
     }
     else
     {
+#if OSL_DEBUG_LEVEL > 0
         xTransporter->getStream().Seek( STREAM_SEEK_TO_END );
         SAL_INFO("extensions.scanner", "Previewbitmapstream contains " << xTransporter->getStream().Tell() << "bytes");
+#endif
         xTransporter->getStream().Seek( STREAM_SEEK_TO_BEGIN );
         mpPreview->SetBitmap(xTransporter->getStream());
     }