Curses: partial stack unselecting

In curses, selecting a partial stack, then unselecting the entry,
and then selecting it normally, the entry still kept the quantity
from the partial selection. Make it behave like all the other
windowports by resetting the quantity when the entry is unselected.

win/curses/cursdial.c

@@ -1636,6 +1636,7 @@ menu_select_deselect(
 
     if (operation == DESELECT || (item->selected && operation == INVERT)) {
         item->selected = FALSE;
+        item->count = -1L;
         if (visible) {
             mvwaddch(win, item->line_num + 1, 1, ' ');
             curses_toggle_color_attr(win, HIGHLIGHT_COLOR, NONE, ON);