Fix use of dangling reference in wxFileSystemWatcher Unix code

Don't reference the "watch" object after possibly destroying it when handling
IN_DELETE_SELF inotify notification.

Closes #17122.

(cherry picked from commit 34d39c9dfb)

docs/changes.txt

@@ -626,6 +626,7 @@ wxGTK:
 - Fix GTK+ warnings when refreshing wxListCtrl items (Scott Talbert).
 - Fix using wxHTTP and wxFTP from worker thread.
 - Make items selected from keyboard visible in wxListCtrl (Jonathan Dagresta).
+- Fix crashes in wxFileSystemWatcher implementation (David Hart).
 
 wxMSW:
 

src/unix/fswatcher_inotify.cpp

@@ -385,6 +385,7 @@ protected:
             // if the wd isn't found: repeated IN_DELETE_SELFs can occur
             wxFileName fn = GetEventPath(watch, inevt);
             wxString path(fn.GetPathWithSep());
+            const wxString filespec(watch.GetFilespec());
 
             if (m_watchMap.erase(inevt.wd) == 1)
             {
@@ -406,7 +407,7 @@ protected:
 
             // Tell the owner, in case it's interested
             // If there's a filespec, assume he's not
-            if (watch.GetFilespec().empty())
+            if (filespec.empty())
             {
                 wxFileSystemWatcherEvent event(flags, fn, fn);
                 SendEvent(event);