abg-dwarf-reader: zero initialize local Dwarf_Addr values

abg-dwarf-reader: zero initialize local Dwarf_Addr values

Not initializing those might lead to undefined behaviour. E.g. if the
call to 'dwarf_ranges' does not initialize 'addr', we pass that
uninitialized value to 'maybe_adjust_fn_sym_address' and test it for
zero as first action, depending on the random value. Hence, fix that by
initializing the values.

	* src/abg-dwarf-reader.cc
	(read_context::get_first_exported_fn_address_from_DW_AT_ranges):
	initialize local Dwarf_Addr variables.

Reviewed-by: Dodji Seketeli <dodji@seketeli.org>
Signed-off-by: Matthias Maennich <maennich@google.com>