There was an addtional div when LogoControl was removed

[jingsam]

mapbox-gl-js version:
0.37.0

Steps to Trigger Behavior

https://jsfiddle.net/jingsam/ue99mkgy/1/

Expected Behavior

there should not exsit a mapbox-ctrl div

Actual Behavior

[jfirebaugh]

Is this causing a particular issue? The logo control is always preset by default; whether it shows anything is dependent on what style you load and your Mapbox account.

[jingsam]

Noop, but I would expect the logo control to be hidden when there were no mapbox sources.

After I checked the logo_control.js, I found the implemention was rather buggy. For example:
https://github.com/mapbox/mapbox-gl-js/blob/master/src/ui/control/logo_control.js#L26
this._updateLogo() would do nothing because the parameter e is undefined

https://github.com/mapbox/mapbox-gl-js/blob/master/src/ui/control/logo_control.js#L47
I think it should be this._map.off('sourcedata', this._updateLogo); Another question is why close the sourcedata event? If users remove all mapbox sources and then readd mapbox sources, this._updateLogo may not fire again.

The logic of _updateLogo is also problematic. When this._logoRequired() is false, the logoControl should be hidden but not to be removed.

I think a simpler and cleaner logic to implement the logoControl is: creating all necessary div and a tag in onAdd, and then if there exists any mapbox sources, display the control; if not, hide this control with display: none

[mollymerp]

@jingsam thanks for the flag. You're right, there are some issues w the logic in LogoControl. I'm working on a PR that I think will address your issues.