Delete this program if it has not already been deleted

Property definitions

gamnit $ GamnitProgram :: delete
	# Delete this program if it has not already been deleted
	fun delete
	do
		if deleted then return

		var gl_program = gl_program
		if gl_program != null then glDeleteProgram gl_program

		deleted = true
	end
lib/gamnit/programs.nit:482,2--491,4