Closes the in-place editor without writing its text, with the rule of
Esc in the VCL grid:
if the text was changed in the editor, only that change is dropped:
the cell shows its value again, and the row stays in edit state if it
already was;
if the text was not changed, the whole row being edited is cancelled
(the dataset’s Cancel), including the values written
earlier in other cells of that row.