This patch resize the nVirtToolBoxHeight in WatchWindow::WatchWindow if
the aRemoveWatchButton plus some space is higher than nVirtToolBoxHeight. So
the aRemoveWatchButton doesn't go into aHeaderBar.

Still room for further improvement.
Includes some fixes for regressions introduced with previous commits.

a) allow blank default prefix
b) select the entire last good prefix is some illegal character used