Fix memort access problems exposed by fuzzed binaries.

Fix memort access problems exposed by fuzzed binaries.

	PR binutils/17531
	* readelf.c (get_unwind_section_word): Skip reloc processing if
	there are no relocs associated with the section.
	(decode_tic6x_unwind_bytecode): Warn and return if the stack
	pointer adjustment falls off the end of the buffer.