Fix variable type

`uint64_t` was causing `idx` to be cast to `uint64_t`, thus
reinterpreting the sign.

Author: kgryte

lib/node_modules/@stdlib/ndarray/base/wrap-index/src/main.c

@@ -33,7 +33,7 @@
 * // returns 2
 */
 int64_t stdlib_ndarray_wrap_index( int64_t idx, int64_t max ) {
-	uint64_t mp1 = max + 1; // `uint64_t` to guard against overflow
+	int64_t mp1 = max + 1; // WARNING: possibility of overflow (although, in practice, `max` should never be that large)
 	if ( idx < 0 ) {
 		idx += mp1; // slight optimization to avoid modulo arithmetic when |idx| <= max+1
 		if ( idx < 0 ) {