lib: libfdt: fdt_region: avoid NULL pointer access

The function fdt_find_regions look in the exclude list for each
property, even if the name is NULL. It could happen if the fit
image is corrupted. On sandbox, it generates a segfault.

To avoid this issue, if the name of a property is NULL, we report
an error and avoid looking in the exclude list.

Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/fdt_region.c b/common/fdt_region.c
index 6676590..ff12c51 100644
--- a/common/fdt_region.c
+++ b/common/fdt_region.c
@@ -65,6 +65,8 @@
 			stop_at = offset;
 			prop = fdt_get_property_by_offset(fdt, offset, NULL);
 			str = fdt_string(fdt, fdt32_to_cpu(prop->nameoff));
+			if (!str)
+				return -FDT_ERR_BADSTRUCTURE;
 			if (str_in_list(str, exc_prop, exc_prop_count))
 				include = 0;
 			break;