fix(storage/spiffs): fix readdir setting errno on directory end (IDFGH-16698)

[augustozanellato]

Description

spiffs_res_to_errno maps SPIFFS_ERR_END_OF_OBJECT to EIO which breaks the common contract where errno should be 0 if readdir iterated through all the entries in a directory.

The fix is explicitly checking for SPIFFS_ERR_END_OF_OBJECT and in that case set errno to 0.

Related

The issue was discovered because a c++ std::filesystem::directory_iterator on a spiffs vfs path threw an std::filesystem::filesystem_error with the following message filesystem error: directory iterator cannot advance: I/O error

Testing

std::filesystem::directory_iterator on a spiffs vfs path now actually works without throwing exceptions

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