fix a warning

Eigen/src/Core/MathFunctions.h

diff --git a/Eigen/src/Core/MathFunctions.h b/Eigen/src/Core/MathFunctions.h
index 9dda28f..cc77799 100644
--- a/Eigen/src/Core/MathFunctions.h
+++ b/Eigen/src/Core/MathFunctions.h
@@ -658,7 +658,7 @@
   static inline Scalar run(Scalar x, Scalar y)
   {
     int res = 1;
-    if(NumTraits<Scalar>::IsSigned) ei_assert(y >= 0);
+    ei_assert(!NumTraits<Scalar>::IsSigned || y >= 0);
     if(y & 1) res *= x;
     y >>= 1;
     while(y)