Bugfix: Correctly check if a cell is registered with the foreign handler.
Bugfix: Correctly check if a cell is registered with the foreign handler.

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