python: imreadmulti - add CV_OUT so it is correctly wrapped

modules/imgcodecs/include/opencv2/imgcodecs.hpp

@@ -173,7 +173,7 @@ The function imreadmulti loads a multi-page image from the specified file into a
 @param mats A vector of Mat objects holding each page, if more than one.
 @sa cv::imread
 */
-CV_EXPORTS_W bool imreadmulti(const String& filename, std::vector<Mat>& mats, int flags = IMREAD_ANYCOLOR);
+CV_EXPORTS_W bool imreadmulti(const String& filename, CV_OUT std::vector<Mat>& mats, int flags = IMREAD_ANYCOLOR);
 
 /** @brief Saves an image to a specified file.