Two missing null check for return values of searchAttributeNyName()

[szsam]

The result of these calls to searchAttributeNyName is not checked for null, but 92% of calls to searchAttributeNyName check for null.

cONNXr/src/operators/ai.onnx/Constant/12/prepare_operator__ai_onnx__constant__12.c

Line 19 in 7108b7b

Onnx__AttributeProto *a_value = searchAttributeNyName(ctx->onnx_node->n_attribute,ctx->onnx_node->attribute,"value");

cONNXr/src/operators/ai.onnx/MaxPool/12/prepare_operator__ai_onnx__maxpool__12.c

Line 26 in 7108b7b

Onnx__AttributeProto *a_kernel_shape = searchAttributeNyName(ctx->onnx_node->n_attribute,ctx->onnx_node->attribute,"kernel_shape");