Return true from wxHyperlinkCtrl::MSWOnNotify()

As SendEvent() not only sends the event about clicking on the link, but
also opens the link in the default browser if this event was not
processed (which wasn't really obvious from its name, so at least
mention it in its comment), the event is actually always handled and so
MSWOnNotify() must return true, not false (and definitely not 0) to
indicate it.

Closes #18266.

include/wx/hyperlink.h

@@ -76,6 +76,9 @@ protected:
     void CheckParams(const wxString& label, const wxString& url, long style);
 
 public:
+    // Send wxHyperlinkEvent and open our link in the default browser if it
+    // wasn't handled.
+    //
     // not part of the public API but needs to be public as used by
     // GTK+ callbacks:
     void SendEvent();