Fix another UB access.

Eigen/src/Core/SolveTriangular.h

diff --git a/Eigen/src/Core/SolveTriangular.h b/Eigen/src/Core/SolveTriangular.h
index 71d6f85..23df508 100644
--- a/Eigen/src/Core/SolveTriangular.h
+++ b/Eigen/src/Core/SolveTriangular.h
@@ -97,6 +97,11 @@
     typedef internal::gemm_blocking_space<(Rhs::Flags&RowMajorBit) ? RowMajor : ColMajor,Scalar,Scalar,
               Rhs::MaxRowsAtCompileTime, Rhs::MaxColsAtCompileTime, Lhs::MaxRowsAtCompileTime,4> BlockingType;
 
+    // Nothing to solve.
+    if (actualLhs.size() == 0 || rhs.size() == 0) {
+      return;
+    }
+
     BlockingType blocking(rhs.rows(), rhs.cols(), size, 1, false);
 
     triangular_solve_matrix<Scalar,Index,Side,Mode,LhsProductTraits::NeedToConjugate,(int(Lhs::Flags) & RowMajorBit) ? RowMajor : ColMajor,

Eigen/src/Core/products/TriangularMatrixMatrix.h

diff --git a/Eigen/src/Core/products/TriangularMatrixMatrix.h b/Eigen/src/Core/products/TriangularMatrixMatrix.h
index 94eabdc..80c98dd 100644
--- a/Eigen/src/Core/products/TriangularMatrixMatrix.h
+++ b/Eigen/src/Core/products/TriangularMatrixMatrix.h
@@ -424,7 +424,7 @@
 
     // Empty product, return early.  Otherwise, we get `nullptr` use errors below when we try to access
     // coeffRef(0,0).
-    if (a_lhs.size() == 0 || a_rhs.size() == 0) {
+    if (lhs.size() == 0 || rhs.size() == 0) {
       return;
     }