Fixed bug (present on Fedora, but not Windows) with DecimalTextCtrl.

The bug fixed by this commit could be produced as follows.

In EntryGroupCtrl, after splitting, in first row (entry), change content
of AccountCtrl, then go into DecimalTextCtrl on that same row and change
content thereof, then SHIFT+TAB back out of that DecimalTextCtrl, and
the AccountCtrl would revert to its original content.