Reduce explicit zeros when applying SparseQR's matrix Q

Eigen/src/SparseQR/SparseQR.h

diff --git a/Eigen/src/SparseQR/SparseQR.h b/Eigen/src/SparseQR/SparseQR.h
index e9b2a6b..267c48b 100644
--- a/Eigen/src/SparseQR/SparseQR.h
+++ b/Eigen/src/SparseQR/SparseQR.h
@@ -573,6 +573,7 @@
         {
           Scalar tau = Scalar(0);
           tau = m_qr.m_Q.col(k).dot(res.col(j));
+          if(tau==Scalar(0)) continue;
           tau = tau * m_qr.m_hcoeffs(k);
           res.col(j) -= tau * m_qr.m_Q.col(k);
         }
@@ -588,6 +589,7 @@
         {
           Scalar tau = Scalar(0);
           tau = m_qr.m_Q.col(k).dot(res.col(j));
+          if(tau==Scalar(0)) continue;
           tau = tau * m_qr.m_hcoeffs(k);
           res.col(j) -= tau * m_qr.m_Q.col(k);
         }