reactor: add an assert for thread context.

Fixes kw warning #13674

Signed-off-by: Seth Howell <seth.howell@intel.com>
Change-Id: I65b8aac045849a8245c6b3e14d853043afdf43a3
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/1986
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Community-CI: Mellanox Build Bot
Reviewed-by: Aleksey Marchuk <alexeymar@mellanox.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>

lib/event/reactor.c

@@ -567,6 +567,8 @@ _reactor_request_thread_reschedule(struct spdk_thread *thread)
 
 	lw_thread = spdk_thread_get_ctx(thread);
 
+	assert(lw_thread != NULL);
+
 	lw_thread->resched = true;
 }