Prevent predux_half for DoublePacket from accidentally catching complex Packets of size >= 16

libeigen/eigen!2125

Eigen/src/Core/products/GeneralBlockPanelKernel.h

diff --git a/Eigen/src/Core/products/GeneralBlockPanelKernel.h b/Eigen/src/Core/products/GeneralBlockPanelKernel.h
index 7238fcd..c2a4eab 100644
--- a/Eigen/src/Core/products/GeneralBlockPanelKernel.h
+++ b/Eigen/src/Core/products/GeneralBlockPanelKernel.h
@@ -650,7 +650,9 @@
 
 template <typename Packet>
 DoublePacket<typename unpacket_traits<Packet>::half> predux_half(
-    const DoublePacket<Packet>& a, std::enable_if_t<unpacket_traits<Packet>::size == 16>* = 0) {
+    const DoublePacket<Packet>& a,
+    std::enable_if_t<unpacket_traits<Packet>::size >= 16 &&
+                     !NumTraits<typename unpacket_traits<Packet>::type>::IsComplex>* = 0) {
   // yes, that's pretty hackish :(
   DoublePacket<typename unpacket_traits<Packet>::half> res;
   typedef std::complex<typename unpacket_traits<Packet>::type> Cplx;