fix(developer): invalid charmap cell selection when updating to empty search result

Fixes #7879.

If we enter a search string that results in zero results, the grid
resize to one row attempts to select row zero. However, we prevent this.
This leaves the current row outside the range of valid rows, which means
the grid is in an invalid state.

This later causes a crash if the user attempts to mousewheel up. There
may be other similar crashes in this situation, but I haven't found any
yet.

Fix is to allow selection of row zero when there is only one row. I have
not found any problems caused by allowing this.