Perform null check before free

[cruzzil]

fitsio/fitsio/fitsio_pywrap.c

Lines 303 to 315 in 9069725

	static struct stringlist* stringlist_delete(struct stringlist* slist) {
	if (slist != NULL) {
	size_t i=0;
	if (slist->data != NULL) {
	for (i=0; i < slist->size; i++) {
	free(slist->data[i]);
	}
	}
	free(slist->data);
	free(slist);
	}
	return NULL;
	}

Line 308, probably want to null check before attempting to free.

Also the free(slist->data); should be inside the conditional block.

[esheldon]

free does nothing if the pointer is NULL