Removing of multiple objects with preserved object stacking

[dkirchhof]

Hello,
i want to delete all currently selected objects at once. Since i set the property preserveObjectStacking to true, it throws an error and deletes just one of the selected objects.
One workaround is to set the flag to false before deleting and set to true again when finished (line 14 & line 19 in the fiddle).

Version

1.7.16

Test Case

https://jsfiddle.net/ak68wm19/1/

Steps to reproduce

1. Open fiddle
2. Select more than one object
3. Press delete

Expected Behavior

All objects should be deleted.

Actual Behavior

Following error will be thrown:

Uncaught TypeError: Cannot read property 'getActiveGroup' of undefined
    at i._renderControls (VM139 fabric.min.js:4)
    at i._renderControls (VM139 fabric.min.js:6)
    at i._renderControls (VM139 fabric.min.js:1)
    at i.drawControls (VM139 fabric.min.js:4)
    at i.renderCanvas (VM139 fabric.min.js:3)
    at i.renderAll (VM139 fabric.min.js:3)
    at i.remove (VM139 fabric.min.js:1)
    at i.remove (VM139 fabric.min.js:4)
    at selection.forEach.obj (VM138:61)
    at Array.forEach (<anonymous>)

[asturur]

i think that removing the objects of the activeGroup trigger some sort of deselection process.
Worth a check.

[asturur]

https://jsfiddle.net/ak68wm19/2/

this can be fixed deleting first the activeGroup and then the objects.
I m working on a fix anyway.

[asturur]

closed with #4120