Fix PDisk SIGSEGV on dangling TLight reference

[SammyVimes]

No description provided.

[github-actions]

⚪ 2025-06-24 23:53:36 UTC Pre-commit check for 35582c8 has started.
⚪ 2025-06-24 23:56:21 UTC Build linux-x86_64-release-asan is running...
🟢 2025-06-25 00:21:36 UTC Build successful.
⚪ 2025-06-25 00:21:54 UTC Tests are running...
🔴 2025-06-25 02:38:48 UTC Some tests failed, follow the links below.

Test history | Test log

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
10972	10850	0	44	28	50

🟢 2025-06-25 02:39:54 UTC ydbd size 5.6 GiB changed* by +2.6 KiB, which is < 100.0 KiB vs stream-nb-24-4: OK

ydbd size dash	stream-nb-24-4: 188cfc1	merge: 35582c8	diff	diff %
ydbd size	6 040 288 464 Bytes	6 040 291 120 Bytes	+2.6 KiB	+0.000%
ydbd stripped size	1 510 870 304 Bytes	1 510 870 688 Bytes	+384 Bytes	+0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}

[github-actions]

⚪ 2025-06-24 23:53:39 UTC Pre-commit check for 35582c8 has started.
⚪ 2025-06-24 23:56:24 UTC Build linux-x86_64-relwithdebinfo is running...
🟢 2025-06-25 00:37:01 UTC Build successful.
⚪ 2025-06-25 00:37:16 UTC Tests are running...
🔴 2025-06-25 02:07:36 UTC Some tests failed, follow the links below.

Test history | Test log

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
15410	14049	0	21	1301	39

🟢 2025-06-25 02:08:35 UTC ydbd size 8.3 GiB changed* by +1.5 KiB, which is < 100.0 KiB vs stream-nb-24-4: OK

ydbd size dash	stream-nb-24-4: 188cfc1	merge: 35582c8	diff	diff %
ydbd size	8 910 534 240 Bytes	8 910 535 808 Bytes	+1.5 KiB	+0.000%
ydbd stripped size	485 665 928 Bytes	485 665 992 Bytes	+64 Bytes	+0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}