PR32109, aborting at bfd/bfd.c:1236 in int _bfd_doprnt

Since bfd_section for .strtab isn't set, print the section index
instead.  Also, don't return NULL on this error as that results in
multiple mmap/read of the string table.  (We could return NULL if we
arranged to set sh_size zero first, but just what we do with fuzzed
object files is of no concern, and terminating the table might make a
faulty object file usable.)

	PR 32109
	* elf.c (bfd_elf_get_str_section): Remove outdated comment, and
	tweak shstrtabsize test to suit.  Don't use string tab bfd_section
	in error message, use index instead.  Don't return NULL on
	unterminated string section, terminate it.
	(_bfd_elf_get_dynamic_symbols): Similarly terminate string table
	section.