bug #1472: fix warning

Eigen/src/Core/Map.h

diff --git a/Eigen/src/Core/Map.h b/Eigen/src/Core/Map.h
index 7ca6a92..c437f1a 100644
--- a/Eigen/src/Core/Map.h
+++ b/Eigen/src/Core/Map.h
@@ -114,7 +114,7 @@
     inline Index outerStride() const
     {
       return StrideType::OuterStrideAtCompileTime != 0 ? m_stride.outer()
-           : internal::traits<Map>::OuterStrideAtCompileTime != Dynamic ? internal::traits<Map>::OuterStrideAtCompileTime
+           : internal::traits<Map>::OuterStrideAtCompileTime != Dynamic ? Index(internal::traits<Map>::OuterStrideAtCompileTime)
            : IsVectorAtCompileTime ? (this->size() * innerStride())
            : int(Flags)&RowMajorBit ? (this->cols() * innerStride())
            : (this->rows() * innerStride());