BUG #18875: COPY BINARY tsvector FROM file leads to misaligned memory access

The following bug has been logged on the website:

Bug reference: 18875
Logged by: Alexander Lakhin
Email address: exclusion(at)gmail(dot)com
PostgreSQL version: 17.4
Operating system: Ubuntu 24.04
Description:

The following script, executed against a build with sanitizers enabled:
CREATE TABLE test_tsvector(t text, a tsvector);
COPY test_tsvector FROM '.../src/test/regress/data/tsearch.data';
COPY BINARY test_tsvector TO '/tmp/t.data';
COPY BINARY test_tsvector FROM '/tmp/t.data';

triggers a runtime error:
2025-04-02 17:23:25.502 UTC [1721608] LOG: statement: COPY BINARY
test_tsvector FROM '/tmp/t.data';
tsvector.c:90:59: runtime error: member access within misaligned address
0x52500005a23c for type 'const struct WordEntryIN', which requires 8 byte
alignment
0x52500005a23c: note: pointer points here
04 00 00 00 04 20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00
^
#0 0x5e62469fe827 in compareentry
.../src/backend/utils/adt/tsvector.c:90
#1 0x5e62469fe85c in WordEntryCMP
.../src/backend/utils/adt/tsvector.c:173
#2 0x5e6246a025bd in tsvectorrecv
.../src/backend/utils/adt/tsvector.c:514
#3 0x5e6246af3bdc in ReceiveFunctionCall
.../src/backend/utils/fmgr/fmgr.c:1715
#4 0x5e6245c759b4 in CopyReadBinaryAttribute
.../src/backend/commands/copyfromparse.c:2048
#5 0x5e6245c7cd0c in CopyFromBinaryOneRow
.../src/backend/commands/copyfromparse.c:1139
#6 0x5e6245c79428 in NextCopyFrom
.../src/backend/commands/copyfromparse.c:890
#7 0x5e6245c6e429 in CopyFrom .../src/backend/commands/copyfrom.c:1149
#8 0x5e6245c669e5 in DoCopy .../src/backend/commands/copy.c:306
#9 0x5e62466463fd in standard_ProcessUtility
.../src/backend/tcop/utility.c:738
...

Reproduced on REL_10_STABLE .. master.