Josep Torra authored Oct 09, 2018 and Olivier Crête committed Oct 10, 2018

This fixes the remaining race condition with the fd by delaying
the removal until last pipe ref.

Unexpected critical/warning: gst_poll_fd_has_error: assertion 'fd->fd
>= 0' failed

Stack trace:
gst_debug_get_stack_trace (gstinfo.c:2788)
gst_check_log_critical_func (gstcheck.c:281)
g_logv (/lib/x86_64-linux-gnu/libglib-2.0.so.0.4800.2:0x7fdd4efa0a40)
g_log (/lib/x86_64-linux-gnu/libglib-2.0.so.0.4800.2:0x7fdd4efa0c6b)
gst_poll_fd_has_error (gstpoll.c:1217)
gst_shm_src_create (gstshmsrc.c:364)
gst_push_src_create (gstpushsrc.c:131)
gst_base_src_get_range (gstbasesrc.c:2521)
gst_base_src_loop (gstbasesrc.c:2845)
gst_task_func (gsttask.c:328)
default_func (gsttaskpool.c:69)

https://bugzilla.gnome.org/show_bug.cgi?id=797203