fix(carousel): uncaught typeerror on empty slides. (#1401)
fix(carousel): uncaught typeerror on empty slides. (#1401)

* Fix carousel error on empty slides.  

Add extra validation for slides Uncaught TypeError: Cannot set property 'tabIndex' of undefined in pause() function

* Fix lint error

* Optimize code

* Update carousel.js

sschadwick/bootstrap-vue,bootstrap-vue/bootstrap-vue,sschadwick/bootstrap-vue,tmorehouse/bootstrap-vue,sschadwick/bootstrap-vue,tmorehouse/bootstrap-vue,bootstrap-vue/bootstrap-vue