WebLogService::operator<< trims with `log_messages_.size() >= limit_log_messages_`.
size() is unsigned, so with limit_log_messages_ == 0 the condition holds even for an
empty deque and pop_front() runs on it - undefined behaviour, in practice heap
corruption. On a PSRAM board the stored value survives a reboot, so the device crashes
again as soon as the first log message is written.
Nothing clamps the value on the way in: start() copies settings.weblog_buffer with no
lower bound, the PSRAM branch of operator<< passes it straight into
limit_log_messages_, and ArduinoJson's | in WebSettings::update() only substitutes the
default for a missing or type-incompatible key - a stored 0 is a valid uint16_t.
- operator<<: skip the trim loop on an empty deque
- start(): keep the existing default when the stored value is 0
- getSetValues(): a missing or zero max_messages keeps the current size instead of
storing 0
- WebSettings::update(): repair a stored 0, and derive the psram/no-psram default once
instead of twice
Refs #3237
