aio-posix: Assert that aio_poll() is always called in home thread

aio_poll() has an existing assertion that the function is only called
from the AioContext's home thread if blocking is allowed.

This is not enough, some handlers make assumptions about the thread they
run in. Extend the assertion to non-blocking calls, too.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

util/aio-posix.c

@@ -613,6 +613,8 @@ bool aio_poll(AioContext *ctx, bool blocking)
     int64_t timeout;
     int64_t start = 0;
 
+    assert(in_aio_context_home_thread(ctx));
+
     /* aio_notify can avoid the expensive event_notifier_set if
      * everything (file descriptors, bottom halves, timers) will
      * be re-evaluated before the next blocking poll().  This is
@@ -621,7 +623,6 @@ bool aio_poll(AioContext *ctx, bool blocking)
      * so disable the optimization now.
      */
     if (blocking) {
-        assert(in_aio_context_home_thread(ctx));
         atomic_add(&ctx->notify_me, 2);
     }