Fix an access through a null pointer when parsing a corrupt SOM format fle.

Fix an access through a null pointer when parsing a corrupt SOM format fle.

	PR 27793
	* som.c (som_slurp_symbol_table): Assign symbols without any scope
	to the undefined section.
	(som_decode_symclass): Check for a missing symbol section.
	* syms.c (bfd_decode_symclass): Likewise.