Fix two asserts in rec_visibility.c

Test failure

ERROR: test_prepare20.test_prepare20.test_prepare20(integer-row.2-26.nocommit) (subunit.RemotedTestCase)

test_prepare20.test_prepare20.test_prepare20(integer-row.2-26.nocommit)

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testtools.testresult.real._StringException: lost connection during test 'test_prepare20.test_prepare20.test_prepare20(integer-row.2-26.nocommit)'

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Ran 8420 tests in 3193.825s

Link: https://evergreen.mongodb.com/task_log_raw/wiredtiger_rhel80_unit_test_9ab4222a555fb209a702ee63c75f22746449b051_22_06_03_07_50_24/0?type=T#L31038

Evergreen YAML Script Failure

Command failed: shell script encountered problem: exit code 1

Link: https://evergreen.mongodb.com/task_log_raw/wiredtiger_rhel80_unit_test_9ab4222a555fb209a702ee63c75f22746449b051_22_06_03_07_50_24/0?type=T#L31045

Verbose Error message

[1654244954:514277][880:0x7f84af8d9700], test_prepare20.test_prepare20.test_prepare20(integer-row.2-26.nocommit), file:prepare20data, eviction-server: [WT_VERB_DEFAULT][ERROR]: __wt_rec_upd_select, 843: upd_select->upd == NULL || !F_ISSET(upd_select->upd, WT_UPDATE_HS) || (!F_ISSET(r, WT_REC_EVICT) && seen_prepare)

[1654244954:514372][880:0x7f84af8d9700], test_prepare20.test_prepare20.test_prepare20(integer-row.2-26.nocommit), file:prepare20data, eviction-server: [WT_VERB_DEFAULT][ERROR]: __wt_abort, 28: aborting WiredTiger library

Link: https://evergreen.mongodb.com/task_log_raw/wiredtiger_rhel80_unit_test_9ab4222a555fb209a702ee63c75f22746449b051_22_06_03_07_50_24/0?type=T#L31233