Need to handle meter not being present

The diagnostics ping test fails with a segfault, as the http_command has a null meter pointer. So, lets find all the places where we access it, and guard against that. I'm assuming meter_ is nullptr when metrics are not enabled, and maybe the ruby defaults such that the meter is always enabled?

Figure it out and fix. For now locally guarding against that in the http_comand.hxx is sufficient to make the tests all pass.