Gaby Dos Reis  <gdr@codesourcery.com>

	* include/bits/basic_string.tcc
	(basic_string::_S_construct(forward_iterator_tag):
	Fix typo in null pointer check.
	* testsuite/21_strings/ctor_copy_dtor.cc: Add test04.

Co-Authored-By: Gabriel Dos Reis <gdr@codesourcery.com>

From-SVN: r54255