Mouse wheel events during click-drag misdelivered as button events

[p-ouellette]

To reproduce, run the mouse demo, click and drag to start drawing a box, then scroll up or down.
Also, in the micro editor you can't start a selection with click-drag, them scroll with the mouse wheel (you can in vim).

The problem is here:

tcell/tscreen.go

Lines 1247 to 1251 in ede1dd5

	if !t.wasbtn {
	button = WheelUp
	} else {
	button = Button1
	}

The wasbtn check seems to be there to work around some terminal bug, but I don't know why. If I remove the check and always report a wheel event the mouse demo and scrolling in micro work as expected.

This can also result in wheel events not during a click-drag being reported as button presses if the tcell application spawns another application on a click event. The child app gets the mouse release event and wasbtn never gets reset.

[gdamore]

Let me think on this -- I am pretty sure that I was seeing drag events that would get misreported. But maybe I've missed something.

[gdamore]

Essentially, I figured that it was not reasonable to scroll while doing drag events - because I was treating the wheel like any other button. That's clearly wrong.

[gdamore]

So I think I must have been confused by the fact that the middle button my mouse (and probably most mice) is also the wheel. The test was wrong, and I'll remove it.

[p-ouellette]

Thanks! The comment above the switch statement could probably be updated too.