build: do not generate empty changelog sections (#14581)
build: do not generate empty changelog sections (#14581)

* Since we filter out duplicate changelog entries it can happen that a `commitGroup` shows up without any commits. e.g. there would be an empty section for `"Features"`.
crisbeto/material2,Jefiozie/material2,andrewseguin/material2,andrewseguin/material2,DevVersion/material2,mmalerba/material2,jelbourn/material2,Jefiozie/material2,josephperrott/material2,mmalerba/material2,mmalerba/material2,josephperrott/material2,andrewseguin/material2,jelbourn/material2,DevVersion/material2,DevVersion/material2,DevVersion/material2,jelbourn/material2,mmalerba/material2,angular/components,mmalerba/material2,josephperrott/material2,andrewseguin/material2,jelbourn/material2,angular/components,jelbourn/material2,angular/components,Jefiozie/material2,josephperrott/material2,DevVersion/material2,crisbeto/material2,crisbeto/material2,andrewseguin/material2,crisbeto/material2,Jefiozie/material2,Jefiozie/material2,angular/components,josephperrott/material2