Fix pooling for large kernel sizes onnx#937

Raise an exception in case an unsupported pooling
operation occurs.

Signed-off-by: Max Huber <maxh@mailbox.org>

onnx2trt_utils.cpp

@@ -1509,6 +1509,8 @@ NodeImportResult poolingHelper(IImporterContext* ctx, ::ONNX_NAMESPACE::NodeProt
     }
 
     nvinfer1::IPoolingLayer* poolingLayer = ctx->network()->addPoolingNd(*tensorPtr, type, kernel_size);
+    ASSERT(poolingLayer && "Failed to add pooling layer.", ErrorCode::kUNSUPPORTED_NODE);
+
     poolingLayer->setStrideNd(strides);
     // This member is ignored in maxpooling
     poolingLayer->setAverageCountExcludesPadding(exclude_padding);