properly size the devices array

modules/core/src/opengl.cpp

@@ -1642,8 +1642,8 @@ Context& initializeContextFromGL()
     NO_OPENCL_SHARING_ERROR;
 #else
     cl_uint numPlatforms;
-    cl_device_id* devices = new cl_device_id[256];
     cl_uint devCnt;
+    cl_device_id* devices;
     cl_uint devUsed;
     cl_context context;
 
@@ -1667,6 +1667,8 @@ Context& initializeContextFromGL()
         if (status != CL_SUCCESS)
             CV_Error_(cv::Error::OpenCLInitError, ("OpenCL: No devices available: %d", status));
 
+        cl_device_id* devices = new cl_device_id[devCnt];
+
         status = clGetDeviceIDs(platforms[i], CL_DEVICE_TYPE_GPU, devCnt, devices, NULL);
         if (status != CL_SUCCESS)
             CV_Error_(cv::Error::OpenCLInitError, ("OpenCL: Can't get platform devices: %d", status));