Before opening, compare String_Contents with entries using stricmp,
selecting the first case-insensitive match. If none matches, set
List_Active_Off and still allow opening. On accepted close, retrieve the
active entry through the Listview and set String_Contents only when an
entry exists. No String_Acknowledge is set here.
Double-click invokes Close(TRUE), whose actual copy occurs later through
Popstring's queued hook. Cancellation leaves the string unchanged. The
popup window and contents follow Popobject ownership and lifecycle
rules.