Fix support for ASA_WVI_1P

[sgerard]

I've fixed some errors regarding the file structure of the product ASA_WVI_1P (bug [EPR-10] on the bug tracker, http://www.brockmann-consult.de/beam-jira/browse/EPR-10). There are also some modifications allowing to open and read files without bands (like ASA_WVI_1P files) and files with dataset descriptors referencing external datasets (not attached to the file).

[avalentino]

In principle the change makes sense but there are points in the code that assume product_id->band_ids to be not NULL, e.g.:

epr-api/src/epr_band.c

Lines 210 to 222 in 4ee3479

	uint epr_get_num_bands(EPR_SProductId* product_id) {
	epr_clear_err();
	if (!epr_check_api_init_flag()) {
	return 0;
	}
	if (product_id == NULL) {
	epr_set_err(e_err_null_pointer,
	"epr_get_num_bands: product_id must not be NULL");
	return (uint) -1;
	}
	return product_id->band_ids->length;
	}

and

epr-api/src/epr_band.c

Lines 224 to 238 in 4ee3479

	EPR_SBandId* epr_get_band_id_at(EPR_SProductId* product_id, uint index) {
	EPR_SBandId* band_id = NULL;
	epr_clear_err();
	if (product_id == NULL) {
	epr_set_err(e_err_null_pointer,
	"epr_get_band_id_at: product_id must not be NULL");
	return NULL;
	}
	if (index >= product_id->band_ids->length) {
	epr_set_err(e_err_index_out_of_range,
	"epr_get_band_id_at: band index out of range");
	return NULL;
	}

[avalentino]

Superseded by #21