PR #1795 changed PacketQueue::countBefore() to use signed 2's complement
arithmetic for millis wraparound safety. However, this broke the
0xFFFFFFFF sentinel pattern used by callers to mean "count all packets
regardless of schedule".
With the signed comparison, countBefore(0xFFFFFFFF) always returns 0,
causing hasPendingWork() to report false and repeaters to sleep with
packets still queued. Stats reporting also shows queue_len as 0.
Add an early-return for the sentinel value before the loop, and document
the sentinel convention on the virtual interface and implementation.
PacketQueue::countBefore() and PacketQueue::get() use unsigned
comparison (_schedule_table[j] > now) to check if a packet is
scheduled for the future. This breaks when millis() wraps around
after ~49.7 days: packets scheduled just before the wrap appear
to be in the far future and get stuck in the queue.
Use signed subtraction instead, matching the approach already used
by Dispatcher::millisHasNowPassed(). This correctly handles the
wraparound for time differences up to ~24.8 days in either
direction, well beyond the maximum queue delay of 32 seconds.
PacketQueue::add() silently dropped packets when the queue was at
capacity. The packet pointer was lost — never enqueued, never returned
to the unused pool. Each occurrence permanently shrank the 32-packet
pool until allocNew() returned NULL and the node went deaf. Return bool
from add() and free the packet back to the pool on failure.
