tests: error out if gtk is available but gtk_init() fails
In case tests are run on a headless system without xvfb then the gtk import will succeed but it will crash in the first gdk/gtk test.
Error out early instead.
Edited by Christoph Reiter
In case tests are run on a headless system without xvfb then the gtk import will succeed but it will crash in the first gdk/gtk test.
Error out early instead.