To reproduce:
1. Open a new project.
2. Create game object.
3. Add "Animation" component.
4. In "Animation" component set "Animations Size" to more than 0.
5. Go to "Animation" window, try pressing on "Create" button. It does not work.

Same result happens if you create animation, then delete it in a Project folder.

Expected result: When you press "Create" it allows you to create a new animation.
Actual result: If "Animations Size" is more than 0, and no Animations are assigned - "Create" button in "Animation" window wont work.

Reproducible with: 5.2.4f1, 5.3.6p7, 5.4.1f1, 5.5.0f3, 5.6.0b3

Additional info:
Lets say, object has 2 animations, 1 is assigned, and the other is not ([no clip]).
If, in "Animation" window [no clip] is selected, it will open same screen with "Create" button. But when "Create" is clicked, it opens animation which is assigned. But it should allow to Create a new animation.
Also, if in "Animation" window [no clip] is selected, the only clickable thing in Animation window is the "Create" button.