Cast matrix size to R_xlen_t to support long vectors

The individual indices for matrices in R are of type int, but the
size is potentially larger than that. R_xlen_t is used for the product
of the number of ros and columns.

Author: rstub

inst/include/RcppEigenWrap.h

@@ -87,7 +87,8 @@ namespace Rcpp{
 																T::ColsAtCompileTime>,
 												  const T&>::type objCopy(obj);
             int m = obj.rows(), n = obj.cols();
-			SEXP ans = PROTECT(::Rcpp::wrap(objCopy.data(), objCopy.data() + m * n));
+			R_xlen_t size = std::static_cast<R_xlen_t>(m) * n;
+			SEXP ans = PROTECT(::Rcpp::wrap(objCopy.data(), objCopy.data() + size));
             if( T::ColsAtCompileTime != 1 ) {
                 SEXP dd = PROTECT(::Rf_allocVector(INTSXP, 2));
                 int *d = INTEGER(dd);