srt: Abort write when epoll fails
When a caller-mode srtsink
gets flushed, the socket is removed from
the poll. This results in gst_srt_object_write_one
entering an endless
loop as srt_epoll_wait
invariably fails.
Do the same handling gst_srt_object_read
does and abort the write in
this case; don't return -1
as that will trigger an element error.