copies: don't record divergence for files needing no merge

This is left over from when _checkcopies was factored out from mergecopies.

The 2nd break has "of = None" before it, so it's a functionally equivalent
change. The 1st one, however, causes a divergence to be recorded when
a file has been renamed, but there is nothing to be merged to it.

This is currently harmless, since the extra divergence is simply ignored
later. However, the new _checkcopies introduced in the rest of this series
does more than just record a divergence after completing the main loop,
and it's important that the "post-processing" stage is really skipped
for no-merge-needed renames.