Fix before-detach in toolbarbutton
Fix before-detach in toolbarbutton

eskirk/jupyterlab,charnpreetsingh185/jupyterlab,TypeFox/jupyterlab,TypeFox/jupyterlab,charnpreetsingh185/jupyterlab,charnpreetsingh185/jupyterlab,jupyter/jupyterlab,charnpreetsingh185/jupyterlab,eskirk/jupyterlab,eskirk/jupyterlab,charnpreetsingh185/jupyterlab,TypeFox/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,TypeFox/jupyterlab,jupyter/jupyterlab,TypeFox/jupyterlab,eskirk/jupyterlab,eskirk/jupyterlab,jupyter/jupyterlab