Fix nested animation name being lost in Collada

[luca-della-vedova]

Hi!

This PR fixes an issue with the name of the animation being empty when parsing nested collada animations. I also added a unit test that fails without the change and succeeds with.
Specifically, the tested collada file has the following animation library:

   <library_animations>
    <animation id="action_container-Armature" name="Armature">
      <animation id="Armature_ArmatureAction_transform" name="Armature">
[...]

Without the change, the animation name is empty, with the change it it set to Armature.

[kimkulling]

Merged, thanks a lot for your contribution.