fix(log_router): stop buffer overrun

[Vincent-Dalstra]

Description

The return value of vsnprintf() is used to determine how long the message was. However, when vsprintf() truncates a message this value will exceed the buffer! Then, vprintf_buffer[len] = '\0'; will cause undefined behaviour.

Add a check for truncation, which will then set the value of len to match the number of bytes in the buffer

Also removed the -1 from the 'size' argument to vsnprintf(), because it already accounts for the terminating '\0' byte.

Testing

I discovered this because my program would always crash after a particular log message. The stack trace showed that something was corrupting the g_esp_log_router_vprintf function pointer and cause any subsequent log messages to panic. Using the ESP32-S3 on-chip debugger I could put a watchpoint on g_esp_log_router_vprintfand thus detect when it was changed by vprintf_buffer[len] = '\0';

After fixing the problem, the program no longer crashes after that message, or other long messages.

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Checklist

Before submitting a Pull Request, please ensure the following:

• 🚨 This PR does not introduce breaking changes.
• All CI checks (GH Actions) pass.
• Documentation is updated as needed.
• Tests are updated or added as necessary.
• Code is well-commented, especially in complex areas.
• Git history is clean — commits are squashed to the minimum necessary.