HTTP dynamic worker scaling is broken in 1.0

[Syraxius]

Hi!

I'd like to bring your attention to the following code section.

	if o.config.workersMax != o.config.workersMin {
		workersCount := int(atomic.LoadInt64(&o.activeWorkers))

		if len(o.queue) > workersCount {
			extraWorkersReq := len(o.queue) - workersCount + 1
			maxWorkersAvailable := o.config.workersMax - workersCount
			if extraWorkersReq > maxWorkersAvailable {
				extraWorkersReq = maxWorkersAvailable
			}
			if extraWorkersReq > 0 {
				o.needWorker <- extraWorkersReq
			}
		}
	}

If not specified, the default values for the worker parameters are as follows:

• workersMax = 0
• workersMin = 0 (even though help hints say default is 1)

At this point, since they're both the same value, then the o.config.workersMax != o.config.workersMin condition will evaluate to false and dynamic scaling is disabled.

Even if we assume the suggested defaults of workersMax = 0, workersMin = 1, we would enter this section but maxWorkersAvailable will always be negative, causing extraWorkersReq to be negative and o.needWorker will never be increased.

Instead, I would suggest this fix:

	if o.config.workersMax != o.config.workersMin || o.config.workersMax == 0 {
		workersCount := int(atomic.LoadInt64(&o.activeWorkers))

		if len(o.queue) > workersCount {
			extraWorkersReq := len(o.queue) - workersCount + 1
			maxWorkersAvailable := o.config.workersMax - workersCount
			if extraWorkersReq > maxWorkersAvailable && o.config.workersMax != 0 {
				extraWorkersReq = maxWorkersAvailable
			}
			if extraWorkersReq > 0 {
				o.needWorker <- extraWorkersReq
			}
		}
	}

Let me know if you're fine with this and I'll submit a PR.

[urbanishimwe]

@Syraxius we're okay with your help