Fix illegal unpack.raw value in __split_ref_move

Verbose Error message

    [1667277011:514840][1139885:0x3ffa99fd910], t, file:T00003.wt, eviction-server: [WT_VERB_DEFAULT][ERROR]: __split_ref_move, 262: encountered an illegal file format or internal value: 0x0: Invalid argument

    [1667277011:514896][1139885:0x3ffa99fd910], t, file:T00003.wt, eviction-server: [WT_VERB_DEFAULT][ERROR]: __split_ref_move, 262: the process must exit and restart: WT_PANIC: WiredTiger library panic

    [1667277011:515076][1139885:0x3ffa99fd910], t, file:T00003.wt, eviction-server: [WT_VERB_DEFAULT][ERROR]: __wt_abort, 28: aborting WiredTiger library

Link: https://evergreen.mongodb.com/task_log_raw/wiredtiger_rhel8_zseries_format_stress_zseries_test_384ced991fa662369dbc0eeaa997e3ef817425c6_22_11_01_00_24_47/0?type=T#L755

Failure keywords

    /data/mci/dcc9853236ad01f7c9db3540b21439cc/wiredtiger/cmake_build/test/format/../../libwiredtiger.so.11.0.1(__wt_panic_func+0x162)[0x3ffab0586a2]

#3  0x000003ffab0586a2 in __wt_panic_func (session=0x3e740540, session@entry=<error reading variable: value has been optimized out>, error=error@entry=22, func=func@entry=0x3ffab0a7466 <__PRETTY_FUNCTION__.18440> "__split_ref_move", line=line@entry=262, category=category@entry=WT_VERB_DEFAULT, fmt=0x3ffab09fadc "%s: 0x%lx") at ../src/support/err.c:570

Link: https://evergreen.mongodb.com/task_log_raw/wiredtiger_rhel8_zseries_format_stress_zseries_test_384ced991fa662369dbc0eeaa997e3ef817425c6_22_11_01_00_24_47/0?type=T#L769