GHSA-58m3-rcvp-f9ww: h2o vulnerable to unexpected POST request shutting down server

In h2oai/h2o-3 version 3.46.0, the run_tool command in the rapids component allows the main function of any class under the water.tools namespace to be called. One such class, MojoConvertTool, crashes the server when invoked with an invalid argument, causing a denial of service.