Fix illegal memory accesses trigeered when linking corrupt input files.

Fix illegal memory accesses trigeered when linking corrupt input files.

	PR 23055
	* aoutx.h (find_nearest_line): Check that the symbol name exists
	and is long enough, before attempting to see if it is for a .o
	file.
	* hash.c (bfd_hash_hash): Add an assertion that the string is not
	NULL.
	* linker.c (bfd_link_hash_lookup): Fail if the table or string are
	NULL.
	(_bfd_generic_link_add_archive_symbols): Fail if an archive entry
	has no name.