Bug fix in solver_impl_test.

One of the tests CreateLinearSolverNoSuiteSparse, fails
when no sparse backend is present. This was a failure
in running tests with all possible sparse backend settings.

Thanks to Sebastian Fabbro for reporting this.

Change-Id: I0ab98632ae7dd33f18d67cb9f490e74c034ce03d

internal/ceres/solver_impl_test.cc

diff --git a/internal/ceres/solver_impl_test.cc b/internal/ceres/solver_impl_test.cc
index 5eb6c66..d918a57 100644
--- a/internal/ceres/solver_impl_test.cc
+++ b/internal/ceres/solver_impl_test.cc
@@ -499,6 +499,8 @@
 TEST(SolverImpl, CreateLinearSolverNoSuiteSparse) {
   Solver::Options options;
   options.linear_solver_type = SPARSE_NORMAL_CHOLESKY;
+  // CreateLinearSolver assumes a non-empty ordering.
+  options.linear_solver_ordering = new ParameterBlockOrdering;
   string error;
   EXPECT_FALSE(SolverImpl::CreateLinearSolver(&options, &error));
 }