win32-aio: Fix memory leak

The buffer is allocated for both reads and writes, and obviously it
should be freed even if an error occurs.

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/win32-aio.c

@@ -87,8 +87,8 @@ static void win32_aio_process_completion(QEMUWin32AIOState *s,
                 memcpy(qiov->iov[i].iov_base, p, qiov->iov[i].iov_len);
                 p += qiov->iov[i].iov_len;
             }
-            qemu_vfree(waiocb->buf);
         }
+        qemu_vfree(waiocb->buf);
     }