replication/driver: simplify second-attempt step correlation code & fix statekeeping
replication/driver: simplify second-attempt step correlation code & fix statekeeping

Before this change, the step correlation code returned early in several cases:
- did not set f.planning.done in the cases where it was a no-op
- did not set f.planning.err in the cases where correlation did not
  succeed

Reported-by: InsanePrawn <e77f743321941e312290b0e6bfb05f89433d2b4a@gmail.com>

zrepl/zrepl,zrepl/zrepl