random.tcc (piecewise_linear_distribution<>:: operator()): Don't crash when the dist is default-constructed.

2010-10-12  Paolo Carlini  <paolo.carlini@oracle.com>

	* include/bits/random.tcc (piecewise_linear_distribution<>::
	operator()): Don't crash when the dist is default-constructed.
	* testsuite/26_numerics/random/piecewise_linear_distribution/
	operators/call-default.cc: New.

From-SVN: r165379