Fixed a warning coming from MSVC in algebra::cmath::vector_getter.

It showed up while trying to build detray with MSVC.

Added code for triggering the issue, so that this project would check
that function explicitly as well. Even if the return value of that
function is not checked. Because that return value is not independent
of the plugin type being used...

math/cmath/include/algebra/math/impl/cmath_getter.hpp

@@ -134,7 +134,7 @@ struct vector_getter {
   ALGEBRA_HOST_DEVICE inline result_type operator()(
       const matrix_type<ROWS, COLS> &m, std::size_t row, std::size_t col) {
 
-    result_type subvector;
+    result_type subvector{};
     for (std::size_t irow = row; irow < row + SIZE; ++irow) {
       subvector[irow - row] = m[col][irow];
     }

tests/common/test_host_basics.hpp

@@ -171,6 +171,11 @@ TYPED_TEST_P(test_host_basics, transform3) {
   auto m44 = trf2.matrix();
   typename TypeParam::transform3 trfm(m44);
 
+  // Make sure that algebra::getter:vector can be called.
+  (void)algebra::getter::vector<3>(m44, 0, 0);
+  (void)algebra::getter::vector<3>(m44, 0, 1);
+  (void)algebra::getter::vector<3>(m44, 0, 2);
+
   // Re-evaluate rot and trn
   auto rotm = trfm.rotation();
   ASSERT_NEAR(element_getter(rotm, 0, 0), x[0], this->m_epsilon);