fix infinite loop

Eigen/src/Core/products/SelfadjointProduct.h

diff --git a/Eigen/src/Core/products/SelfadjointProduct.h b/Eigen/src/Core/products/SelfadjointProduct.h
index 9eb5de7..35d5ded 100644
--- a/Eigen/src/Core/products/SelfadjointProduct.h
+++ b/Eigen/src/Core/products/SelfadjointProduct.h
@@ -75,7 +75,8 @@
     Index nc = size;  // cache block size along the N direction
     computeProductBlockingSizes<Scalar,Scalar>(kc, mc, nc);
     // !!! mc must be a multiple of nr:
-    mc = (mc/Blocking::nr)*Blocking::nr;
+    if(mc>Blocking::nr)
+      mc = (mc/Blocking::nr)*Blocking::nr;
 
     Scalar* blockA = ei_aligned_stack_new(Scalar, kc*mc);
     std::size_t sizeB = kc*Blocking::PacketSize*Blocking::nr + kc*size;