MoreCast2: Clear datagrid when station group cleared

**Actual Behaviour**

When I have selected a station group I see station data in the datagrid. If I clear the station group the list of stations disappears, but station data remains visible in the datagrid.


**Expected Behaviour**

When no station group is selected, the datagrid is empty.

No file, test, or entry point is named. Start by locating the MoreCast2 station-group selection and datagrid components, reproduce clearing a selected group, and confirm that the datagrid is empty when no station group remains selected.

Written by the indexing model from the issue text.