asan: NULL deref in scan_unit_for_symbols

Since commit b43771b045 it has been possible to look up addresses
that match a unit with errors, since ranges are added to a trie while
the unit is being parsed.  On error, parse_comp_unit leaves
first_child_die_ptr NULL which results in a NULL info_ptr being passed
to scan_unit_for_symbols.  Fix this by setting unit->error.

Also wrap some overlong lines, and fix some formatting errors.

	* dwarf2.c: Formatting.
	(parse_comp_unit): Set unit->error on err_exit path.