Connections can crash when KeepAlive stops a CommandRunner

[Ben Youngblood]

Sentry.CrashError: ** (exit) exited in: GenServer.stop(#PID<0.8812.47>, :normal, :infinity)
    ** (EXIT) no process: the process is not alive or there's no process currently associated with the given name, possibly because its application isn't started
  File "lib/gen_server.ex", line 995, in GenServer.stop/3
  File "lib/grizzly/connections/keep_alive.ex", line 100, in Grizzly.Connections.KeepAlive.maybe_stop_command_runner/1
  File "lib/grizzly/connections/keep_alive.ex", line 78, in Grizzly.Connections.KeepAlive.timer_restart/1
  File "lib/grizzly/connections/sync_connection.ex", line 221, in Grizzly.Connections.SyncConnection.do_handle_commands/2
  File "lib/grizzly/connections/sync_connection.ex", line 139, in Grizzly.Connections.SyncConnection.handle_info/2
  File "gen_server.erl", line 1123, in :gen_server.try_dispatch/4
  File "gen_server.erl", line 1200, in :gen_server.handle_msg/6
  File "proc_lib.erl", line 240, in :proc_lib.init_p_do_apply/3