libstdc++: Fix deserialization for std::normal_distribution [PR105502]

libstdc++: Fix deserialization for std::normal_distribution [PR105502]

This fixes a regression in std::normal_distribution deserialization that
caused the object to be left unchanged if the __state_avail value read
from the stream was false.

libstdc++-v3/ChangeLog:

	PR libstdc++/105502
	* include/bits/random.tcc
	(operator>>(basic_istream<C,T>&, normal_distribution<R>&)):
	Update state when __state_avail is false.
	* testsuite/26_numerics/random/normal_distribution/operators/serialize.cc:
	Check that deserialized object equals serialized one.