added release method to GMG_GPU

modules/gpu/src/bgfg_gmg.cpp

@@ -47,6 +47,7 @@
 cv::gpu::GMG_GPU::GMG_GPU() { throw_nogpu(); }
 void cv::gpu::GMG_GPU::initialize(cv::Size, float, float) { throw_nogpu(); }
 void cv::gpu::GMG_GPU::operator ()(const cv::gpu::GpuMat&, cv::gpu::GpuMat&, float, cv::gpu::Stream&) { throw_nogpu(); }
+void cv::gpu::GMG_GPU::release() {}
 
 #else
 
@@ -151,4 +152,15 @@ void cv::gpu::GMG_GPU::operator ()(const cv::gpu::GpuMat& frame, cv::gpu::GpuMat
     ++frameNum_;
 }
 
+void cv::gpu::GMG_GPU::release()
+{
+    frameSize_ = Size();
+
+    nfeatures_.release();
+    colors_.release();
+    weights_.release();
+    boxFilter_.release();
+    buf_.release();
+}
+
 #endif