Allow disabling saving wxFileConfig data when it is destroyed

This can be useful to avoid saving the changes performed by the user if
this turns out to be undesirable, for whatever reason.

Closes https://github.com/wxWidgets/wxWidgets/pull/1451

Closes #13788.

src/common/fileconf.cpp

@@ -346,6 +346,7 @@ void wxFileConfig::Init()
     }
 
     m_isDirty = false;
+    m_autosave = true;
 }
 
 // constructor supports creation of wxFileConfig objects of any type
@@ -487,7 +488,8 @@ void wxFileConfig::CleanUp()
 
 wxFileConfig::~wxFileConfig()
 {
-    Flush();
+    if ( m_autosave )
+        Flush();
 
     CleanUp();