When you create in logging subsystem configuration an async handler with positive queue length value and then try to edit the queue length value to 0 it is successfully saved in web console, not in model, and after refreshing the previous queue length value is shown.
When you try to set 0 value through CLI with /subsystem=logging/async-handler=sda:write-attribute(name=queue-length,value=0) it shows error

{
    "outcome" => "failed",
    "failure-description" => "WFLYCTL0117: 0 is an invalid value for parameter queue-length. A minimum value of 1 is required",
    "rolled-back" => true,
    "response-headers" => {"process-state" => "reload-required"}
}