Log progress while verifying blocks at level 4.
Log progress while verifying blocks at level 4.

When verifying blocks at startup, the progress is printed in 10%
increments to logs.  When -checklevel=4, however, the second half
of the verification (connecting the blocks again) does not log the
progress anymore.  (It is still computed and shown in the UI, but
not printed to logs.)

This change makes the behaviour consistent, by adding the missing
progress logging also for level-4 checks.

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