asan: null dereference in read_and_display_attr_value

This fixes multiple places in read_and_display_attr_value dealing with
range and location lists that can segfault when debug_info_p is NULL.
Fuzzed object files can contain arbitrary DW_FORMs.

	* dwarf.c (read_and_display_attr_value): Don't dereference NULL
	debug_info_p.