Do not crash if OpenGL is not usable

[claunia]

Eto.Forms.SkiaSharp/Eto.Forms.Controls.SkiaSharp.GTK/SKGLControl.cs

Line 62 in f3e6368

Console.WriteLine("Error creating OpenGL ES interface. Check if you have OpenGL ES correctly installed and configured or change the PFD Renderer to 'Software (CPU)' on the Global Settings panel.", "Error Creating OpenGL ES interface");

Should just raise a exception, so the application knows "GL is not available, let's use SKControl instead". If the application does not catch the exception the end result would be the same.