Do not attempt to fetch conflict details in the conflict scenario described in issue #4744, where merge-left and merge-right URLs differ and their peg revisions are the same. The 'merge directories' resolution option does not handle this case yet (and is no longer offered in this case since r1833897).
However, the 'replace + merge' option works as expected. For now this is good enough, and certainly better than an assertion failure. Making the 'merge directories' option work is left for future work.
* subversion/libsvn_client/conflicts.c (conflict_tree_get_details_incoming_add): Don't return details in case merge-left/right URLs do not match and/or old_rev == new_rev.
* subversion/tests/libsvn_client/conflicts-test.c (test_merge_two_added_dirs_assertion_failure): Resolve by replace + merge and update test expectations accordingly.