Problem with invert_match and select_by_key

[Denis Puthier]

	from pygtftk.utils import get_example_file
	from pygtftk.gtf_interface import GTF
	a_file = get_example_file("simple", "gtf")[1]
	gtf = GTF(a_file)

	gtf_data_2 = gtf._dll.select_by_key(gtf._data, "feature", "exon", 1)
	gtf_data_2 = gtf._dll.select_by_key(gtf._data, "feature", "exon", 0)
	python(99002,0x7fff70ef4000) malloc: *** error for object 0x7f8e7eb78720: pointer being freed was not allocated
	*** set a breakpoint in malloc_error_break to debug
	Abort trap: 6