Typo: loop on all Marks instead of processing Mark(0) over and over

See:

http://nabble.documentfoundation.org/Suspicious-loop-any-idea-td4119239.html

Since the code was like this since initial import (2000), if this patch proves
to be wrong then the other option could be to just don't loop and process
Mark(0) just once.

Change-Id: I41ac18604e916740dcc68bf69af37529842f774d