resolver adds unrelated moves to move target list

The resolver adds unrelated moves to the move target list in some situations, leading it to suggest bogus move targets in the working copy.

This problem was introduced in https://svn.apache.org/r1806822

diff: https://svn.apache.org/viewvc/subversion/trunk/subversion/libsvn_client/conflicts.c?r1=1806822&r2=1806821&pathrev=1806822
 
Note how the new code is pushing moves onto the list even if relpath is NULL.