Abort if the stage could not be created

[aalex]

aalex@plank:~/src/toonloop$ ./src/toonloop -d test
video-source is set to test
project-home is set to /home/aalex/Documents/toonloop/default
The initial frame rate for clip playhead is set to 12
Xlib:  extension "GLX" missing on display ":0.0".
Xlib:  extension "GLX" missing on display ":0.0".
Starting GUI.

(toonloop:1976): Clutter-WARNING **: Unable to create a new stage: the glx backend does not support multiple stages.

(toonloop:1976): GLib-GObject-WARNING **: invalid (NULL) pointer instance

(toonloop:1976): GLib-GObject-CRITICAL **: g_signal_connect_data: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed

(toonloop:1976): Clutter-CRITICAL **: clutter_stage_set_user_resizable: assertion `CLUTTER_IS_STAGE (stage)' failed

(toonloop:1976): GLib-GObject-WARNING **: invalid (NULL) pointer instance

(toonloop:1976): GLib-GObject-CRITICAL **: g_signal_connect_data: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed

(toonloop:1976): Clutter-CRITICAL **: clutter_stage_set_minimum_size: assertion `CLUTTER_IS_STAGE (stage)' failed
Segmentation fault