Remove useless test in determinant

Also add a LCOV_EXCL_LINE marker. lcov produced a false negative probably due to
a forced inline.

src/algebra/TinyMatrix.hpp

@@ -20,8 +20,7 @@ class TinyMatrix
   static_assert((N > 0), "TinyMatrix size must be strictly positive");
 
   PUGS_FORCEINLINE
-  constexpr size_t
-  _index(const size_t& i, const size_t& j) const noexcept
+  constexpr size_t _index(const size_t& i, const size_t& j) const noexcept   // LCOV_EXCL_LINE (due to forced inline)
   {
     return i * N + j;
   }
@@ -344,8 +343,6 @@ det(const TinyMatrix<N, T>& A)
       }
     }
     const size_t I  = index[i];
-    if (M(I, i) == 0)
-      return 0;
     const T inv_Mii = 1. / M(I, i);
     for (size_t k = i + 1; k < N; ++k) {
       const size_t K = index[k];