[Fix][Crash] races on timers

Change-Id: I8979882e5b544cc98532d641ea31bcfe0ac3483c

Author: crichard

src/internal/sio_client_impl.cpp

@@ -632,11 +632,16 @@ namespace sio
  }
 
  void client_impl::reset_timer(TIMER &timer) {
- if (timer)
- {
- timer->cancel();
- timer.reset();
- }
+ // Atomically take ownership of the timer pointer before operating on
+ // it. Without this, a concurrent caller (e.g. another reset_timer /
+ // update_timer on the same field, or a TimerManager callback racing
+ // with on_close's clear_timers) could pass the null check while we
+ // are mid-destroy and crash dereferencing a freed timer.
+ if (auto* t = timer.release())
+ {
+ t->cancel();
+ delete t;
+ }
  }
 
  void client_impl::update_send_timer() {