rebase: fix crash with in-memory rebase and copies When using regular on-disk rebase, filectx.markcopies() calls to dirstate.copy(), which happily records the copy. Then it's simply ignored if it doesn't matter for the commit (as in the test case I added in the previous patch). Let's do the same for overlayworkingctx. Differential Revision: https://phab.mercurial-scm.org/D6133