Segfault in reconciliation during checkpoint

Backtrace:

/home/jenkins/jenkins/workspace/wiredtiger-test-format-stress/build_posix/../src/reconcile/rec_write.c:4260(__rec_row_merge)[0x457c46]

/home/jenkins/jenkins/workspace/wiredtiger-test-format-stress/build_posix/../src/reconcile/rec_write.c:4146(__rec_row_int)[0x4576dc]

/home/jenkins/jenkins/workspace/wiredtiger-test-format-stress/build_posix/../src/reconcile/rec_write.c:409(__wt_reconcile)[0x44fe9d]

/home/jenkins/jenkins/workspace/wiredtiger-test-format-stress/build_posix/../src/btree/bt_sync.c:165(__sync_file)[0x49ed19]

/home/jenkins/jenkins/workspace/wiredtiger-test-format-stress/build_posix/../src/btree/bt_sync.c:256(__wt_cache_op)[0x49ef59]

/home/jenkins/jenkins/workspace/wiredtiger-test-format-stress/build_posix/../src/txn/txn_ckpt.c:981(__checkpoint_worker)[0x47863d]

/home/jenkins/jenkins/workspace/wiredtiger-test-format-stress/build_posix/../src/txn/txn_ckpt.c:1063(__wt_checkpoint)[0x478952]

/home/jenkins/jenkins/workspace/wiredtiger-test-format-stress/build_posix/../src/txn/txn_ckpt.c:184(__checkpoint_apply)[0x4762f4]

/home/jenkins/jenkins/workspace/wiredtiger-test-format-stress/build_posix/../src/txn/txn_ckpt.c:464(__wt_txn_checkpoint)[0x47736b]

/home/jenkins/jenkins/workspace/wiredtiger-test-format-stress/build_posix/../src/session/session_api.c:912(__session_checkpoint)[0x469dee]

/home/jenkins/jenkins/workspace/wiredtiger-test-format-stress/build_posix/test/format/../../../test/format/ops.c:351(ops)[0x40f691]

############################################

#  RUN PARAMETERS

############################################

abort=0

auto_throttle=1

firstfit=0

bitcnt=1

bloom=1

bloom_bit_count=14

bloom_hash_count=15

bloom_oldest=0

cache=63

checkpoints=1

checksum=off

chunk_size=4

compaction=0

compression=lz4

data_extend=0

data_source=table

delete_pct=20

dictionary=0

evict_max=0

file_type=row-store

backups=0

huffman_key=0

huffman_value=0

insert_pct=20

internal_key_truncation=1

internal_page_max=15

isolation=random

key_gap=15

key_max=98

key_min=10

leak_memory=0

leaf_page_max=10

logging=0

logging_archive=0

logging_prealloc=0

lsm_worker_threads=4

merge_max=12

mmap=1

ops=100000

prefix_compression=1

prefix_compression_min=8

repeat_data_pct=38

reverse=0

rows=100000

runs=100

split_pct=53

statistics=0

statistics_server=0

threads=10

timer=20

value_max=3618

value_min=7

wiredtiger_config=

write_pct=13

############################################