Imply type of literal returned based on input protobuff for zero element constant values.

This saves us the default behavior as the onnx parsing assumes that every zero value is float. This way we're still grabbing relevant type information from the protobuff instead and wont fail our data type checks for if them/else blocks from onnx

src/onnx/parse_constant.cpp

@@ -39,11 +39,13 @@ struct parse_constant : op_parser<parse_constant>
                           onnx_parser::node_info info,
                           const std::vector<instruction_ref>& /*args*/) const
     {
+
         literal v = parser.parse_value(info.attributes.at("value"));
         // return empty literal
         if(v.get_shape().elements() == 0)
         {
-            return info.add_literal(literal{});
+            auto dim_param = info.attributes.at("value").t().dims();
+            return info.add_literal(literal{dim_param.at(0)});
         }
 
         auto dim_size = info.attributes.at("value").t().dims_size();