Fix optional columns handling in read_rows rpc (#15850)

[dcherednik]

bring bugfix from #15850

Changelog category

• Bugfix

Description for reviewers

...

[github-actions]

⚪ 2025-06-02 17:19:30 UTC Pre-commit check for 81a1a84 has started.
⚪ 2025-06-02 17:22:13 UTC Build linux-x86_64-release-asan is running...
🔴 2025-06-02 17:25:15 UTC Build failed. see the build logs.
🔴 2025-06-02 17:25:17 UTC Tests run skipped.

[github-actions]

⚪ 2025-06-02 17:19:33 UTC Pre-commit check for 81a1a84 has started.
⚪ 2025-06-02 17:22:14 UTC Build linux-x86_64-relwithdebinfo is running...
🔴 2025-06-02 17:25:13 UTC Build failed. see the build logs.
🔴 2025-06-02 17:25:14 UTC Tests run skipped.

[github-actions]

⚪ 2025-06-02 18:13:04 UTC Pre-commit check for 4b15f31 has started.
⚪ 2025-06-02 18:15:48 UTC Build linux-x86_64-relwithdebinfo is running...
🟢 2025-06-02 18:57:41 UTC Build successful.
⚪ 2025-06-02 18:58:04 UTC Tests are running...
🔴 2025-06-02 20:33:11 UTC Some tests failed, follow the links below.

Test history | Test log

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
14863	13498	0	23	1302	40

🟢 2025-06-02 20:34:11 UTC ydbd size 8.3 GiB changed* by +11.1 KiB, which is < 100.0 KiB vs stream-nb-24-4: OK

ydbd size dash	stream-nb-24-4: 2f84896	merge: 4b15f31	diff	diff %
ydbd size	8 910 258 992 Bytes	8 910 270 320 Bytes	+11.1 KiB	+0.000%
ydbd stripped size	485 655 432 Bytes	485 656 584 Bytes	+1.1 KiB	+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]

⚪ 2025-06-02 18:13:43 UTC Pre-commit check for 4b15f31 has started.
⚪ 2025-06-02 18:16:45 UTC Build linux-x86_64-release-asan is running...
🟢 2025-06-02 18:39:18 UTC Build successful.
⚪ 2025-06-02 18:39:32 UTC Tests are running...
🔴 2025-06-02 20:50:19 UTC Some tests failed, follow the links below.

Test history | Test log

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
10436	10313	0	47	33	43

🟢 2025-06-02 20:51:05 UTC ydbd size 5.6 GiB changed* by +16.9 KiB, which is < 100.0 KiB vs stream-nb-24-4: OK

ydbd size dash	stream-nb-24-4: 2f84896	merge: 4b15f31	diff	diff %
ydbd size	6 040 020 544 Bytes	6 040 037 888 Bytes	+16.9 KiB	+0.000%
ydbd stripped size	1 510 808 224 Bytes	1 510 813 088 Bytes	+4.8 KiB	+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}