More fixes for problems exposed by valgrind and the address sanitizer

More fixes for problems exposed by valgrind and the address sanitizer
when displaying the contents of corrupt files.

	PR binutils/17521
	* coff-i386.c (NUM_HOWTOS): New define.
	(RTYPE2HOWTO): Use it.
	(coff_i386_rtype_to_howto): Likewise.
	(coff_i386_reloc_name_lookup): Likewise.
	(CALC_ADDEND): Check that reloc r_type field is valid.
	* coff-x86_64.c (NUM_HOWTOS): New define.
	(RTYPE2HOWTO): Use it.
	(coff_amd64_rtype_to_howto): Likewise.
	(coff_amd64_reloc_name_lookup): Likewise.
	(CALC_ADDEND): Check that reloc r_type field is valid.
	* coffcode.h (coff_slurp_line_table): Check for symbol table
	indexing underflow.
	(coff_slurp_symbol_table): Use zalloc to ensure that all table
	entries are initialised.
	* coffgen.c (_bfd_coff_read_string_table): Initialise unused bits
	in the string table.  Also ensure that the table is 0 terminated.
	(coff_get_normalized_symtab): Check for symbol table indexing
	underflow.
	* opncls.c (bfd_alloc): Catch the case where a small negative size
	can result in only 1 byte being allocated.
	(bfd_alloc2): Use bfd_alloc.
	* pe-mips.c (NUM_HOWTOS): New define.
	(coff_mips_reloc_name_lookup): Use it.
	(CALC_ADDEND): Check that reloc r_type field is valid.
	* peXXigen.c (_bfd_XXi_swap_aouthdr_in): Initialise unused entries
	in the DataDirectory.
	(pe_print_idata): Avoid reading beyond the end of the data block
	wen printing strings.
	(pe_print_edata): Likewise.
	Check for table indexing underflow.
	* peicode.h (pe_mkobject): Initialise the pe_opthdr field.
	(pe_bfd_object_p): Allocate and initialize enough space to hold a
	PEAOUTHDR, even if the opt_hdr field specified less.