Bug when opening a second modal if the first one is still clossing

[pjmolina]

Hi.
I have found the following case: two or more consecutive modals must be shown (like wizard steps).
If you open a second modal when the first one is still closing, the UI freezes.

Repro sample: https://stackblitz.com/edit/ng2-bs3-modal-case

See app/app-component.ts line 32 for second opening when the first one is still closing.

Current work-around: avoid opening the second modal till ensuring the first one is fully closed.
In this simple case, it is fixed moving the logic from second opening from line 32 to 24 modalClosed().

However, I think this is a bug and should be fixed in the way, the library should properly deal with open and closing in safe and reliable ways, delaying opening if needed.