fix nasty off by one error that put the end of an end-trimmed region one sample beyon...

fix nasty off by one error that put the end of an end-trimmed region one sample beyond where it should be. this would lead to the creation of 1 sample xfades where there should be none, if another region was aligned to the same point that the region had been nomimally trimmed to

git-svn-id: svn://localhost/ardour2/branches/3.0@10541 d708f5d6-7413-0410-9779-e7cbd77b26cf