Ensure the Cuda context is initialized correctly as long as the setDevice is not…

Ensure the Cuda context is initialized correctly as long as the setDevice is not called in a multi-thread environment.

modules/core/src/cuda_info.cpp

@@ -70,6 +70,7 @@ void cv::cuda::setDevice(int device)
     (void) device;
     throw_no_cuda();
 #else
+    cudaFree(0);
     cudaSafeCall( cudaSetDevice(device) );
 #endif
 }