CellRenderer_TimeTrack now uses TimePlotData too

[rodolforg]

No description provided.

[ice0]

There is an error if run synfigstudio and quit.

(synfigstudio:31625): Gtk-CRITICAL **: 07:57:24.159: gtk_widget_queue_draw: assertion 'GTK_IS_WIDGET (widget)' failed

You can debug it with G_DEBUG environment variable.
G_DEBUG=fatal-criticals

P.S. The problem was introduced by this PR (#2382)

backtrace:

g_logv 0x00007f3c8d709579
g_log 0x00007f3c8d709743
gtk_widget_queue_draw 0x00007f3c8de3083d
studio::TimePlotData::queue_draw timeplotdata.cpp:206
studio::TimePlotData::recompute_time_bounds timeplotdata.cpp:139
studio::TimePlotData::set_time_model timeplotdata.cpp:101
studio::Widget_Keyframe_List::set_time_model widget_keyframe_list.cpp:442
studio::Widget_Keyframe_List::~Widget_Keyframe_List widget_keyframe_list.cpp:124
studio::Widget_Keyframe_List::~Widget_Keyframe_List widget_keyframe_list.cpp:127
...

[rodolforg]

P.S. The problem was introduced by this PR (#2382)

Done #2388

[ice0]

Merged. Thank you!