gstclock: segmentation fault when unschedule

Submitted by Miguel París Díaz @mparisdiaz

Link to original bug (#770953)

Description

Hello,
I have found a segmentation fault when gst_clock_id_unschedule is called.

Debugging with GDB I found that it is caused in the line [1].
From this info and analysing the code, it seems that gst_clock_entry_new [2] does not increase the ref of the clock used, it just keeps the pointer.
So I suppose that the problem is that the clock has been released when gst_clock_id_unschedule is called.

What do you think about that?

Refs
[1] https://github.com/Kurento/gstreamer/blob/0fb3a083ce04551fbdba7a94f0ac5612515bda67/gst/gstclock.c#L667
[2] https://github.com/Kurento/gstreamer/blob/0fb3a083ce04551fbdba7a94f0ac5612515bda67/gst/gstclock.c#L243

Version: 1.8.3