A button with an additional description but a empty description is display with uncessary breakline.

See on "paste content values" button when the bouton is disabled because the target content is not modifiable.

In #_getTooltip() function of CommonController, the tooltip text is built as following :
this._description + (this._additionalDescription ? ('<br/><br/>' + this._additionalDescription) : '')

The <br/> should be added only if description is not empty.