[TLV Read] - fix read resetting empty TLV data (backport #43182)

[mergify]

Summary

• TLV getting data pointer returns null on empty length:

CHIP_ERROR TLVReader::GetDataPtr(const uint8_t *& data) const
{
    VerifyOrReturnError(TLVTypeIsString(ElementType()), CHIP_ERROR_WRONG_TLV_TYPE);

    if (GetLength() == 0)
    {
        data = nullptr;
        return CHIP_NO_ERROR;
    }
    ...

This results in checks for data pointer to early return and were failing to reset the CharSpan to an empty value. This breaks any code that assumes a successful read will reset the data (which seems reasonable).

We mostly did not see it because we often initialize CharSpan and then read. Correctness-wise though, a successfull read should update the read target.

Testing

CI tests updated to a test that would catch this bug (tested that it would fail before the fix)

---

This is an automatic backport of pull request #43182 done by Mergify.

[github-actions]

PR #72389: Size comparison from 09d0453 to 5fec415

Full report (14 builds for cc13x4_26x4, cc32xx, nrfconnect, qpg, stm32, tizen)

platform	target	config	section	09d0453	5fec415	change	% change
cc13x4_26x4	lighting-app	LP_EM_CC1354P10_6	FLASH	764852	764860	8	0.0
			RAM	103376	103376	0	0.0
	lock-ftd	LP_EM_CC1354P10_6	FLASH	776656	776664	8	0.0
			RAM	108560	108560	0	0.0
	pump-app	LP_EM_CC1354P10_6	FLASH	722620	722628	8	0.0
			RAM	96948	96948	0	0.0
	pump-controller-app	LP_EM_CC1354P10_6	FLASH	706912	706920	8	0.0
			RAM	97156	97156	0	0.0
cc32xx	air-purifier	CC3235SF_LAUNCHXL	FLASH	550146	550146	0	0.0
			RAM	205176	205176	0	0.0
	lock	CC3235SF_LAUNCHXL	FLASH	583386	583394	8	0.0
			RAM	205384	205384	0	0.0
nrfconnect	all-clusters-app	nrf52840dk_nrf52840	FLASH	916480	916488	8	0.0
			RAM	167458	167458	0	0.0
	all-clusters-minimal-app	nrf52840dk_nrf52840	FLASH	859992	860000	8	0.0
			RAM	141065	141065	0	0.0
	all-clusters-app	nrf7002dk_nrf5340_cpuapp	FLASH	914452	914460	8	0.0
			RAM	145676	145676	0	0.0
qpg	lighting-app	qpg6200+debug	FLASH	745088	745104	16	0.0
			RAM	94228	94228	0	0.0
	lock-app	qpg6200+debug	FLASH	755044	755044	0	0.0
			RAM	94264	94264	0	0.0
stm32	light	STM32WB5MM-DK	FLASH	466512	466520	8	0.0
			RAM	141376	141376	0	0.0
tizen	all-clusters-app	arm	unknown	5308	5308	0	0.0
			FLASH	1822368	1822392	24	0.0
			RAM	97556	97556	0	0.0
	chip-tool-ubsan	arm	unknown	20700	20700	0	0.0
			FLASH	20976754	20976874	120	0.0
			RAM	9131396	9131460	64	0.0