Fix compile time warnings about the possibility of using uninitialised fields...

Fix compile time warnings about the possibility of using uninitialised fields in the Elf_Internal_Chdr structure when building readelf.

	* readelf.c (get_compression_header): Add ATTRIBUTE_WARN_UNUSED_RESULT.
	(process_section_headers): Check the return value from
	get_compression_header.
	(dump_section_as_strings): Likewise.
	(dump_section_as_bytes): Likewise.
	(load_specific_debug_section): Likewise.