Fix consume status of mouse events in custom capture

[GiGurra]

At present, it is not possible to consume events in the mouse event capture function, even if you return nil. This causes (among other things) Application.draw() to not fire properly, and essentially, means that any gui state changes you make inside the capture function, isn't rendered.

This PR hopefully fixes that. I couldn't find any tests to modify/change, do you need any other info?

The following code (from the Application event loop) shows where the draw call would be skipped when the wrong consume status is returned

case *tcell.EventMouse:
	consumed, isMouseDownAction := a.fireMouseActions(event)
	if consumed {
		a.draw()
	}
	a.lastMouseButtons = event.Buttons()
	if isMouseDownAction {
		a.mouseDownX, a.mouseDownY = event.Position()
	}

[rivo]

See #972 (comment) for details.