Fix bug with not re-enabling wxStaticBox with label sometimes

In some specific scenario, described in the newly added comment in
wxStaticBoxBase::Enable(), the box and its label could remain disabled
after its parent was disabled and re-enabled.

Fix this by continuing to use the derived class version for disabling
the box children, but not when enabling them, as the base class version
already does the right thing in this case.

src/common/statboxcmn.cpp

@@ -94,7 +94,26 @@ bool wxStaticBoxBase::Enable(bool enable)
     // in this case and only disable its children, but still pretend that the
     // box is disabled by updating its m_isEnabled, as it would be surprising
     // if IsEnabled() didn't return false after disabling the box, for example.
-    if ( m_labelWin )
+    //
+    // Finally note that this really needs to be done only when disabling the
+    // box and not when re-enabling it, at least for the platforms without
+    // native enabled state management (e.g. wxMSW) because otherwise we could
+    // have a bug in the following scenario:
+    //
+    //  0. The box is initially enabled
+    //  1. Its parent gets disabled, calling DoEnable(false) on the box and all
+    //     its children from its NotifyWindowOnEnableChange() (including the
+    //     label).
+    //  2. The box is itself disabled (for whatever app logic reason).
+    //  3. The parent gets enabled but this time doesn't do anything with the
+    //     box, because it should continue being disabled.
+    //  4. The box is re-enabled -- but remains actually disabled as
+    //     DoEnable(true) was never called on it (nor on the label).
+    //
+    // To avoid this possibility, we always call the base class version, which
+    // does call DoEnable(true) on the box itself and all its children,
+    // including the label, when re-enabling it.
+    if ( m_labelWin && !enable )
     {
         if ( enable == IsThisEnabled() )
             return false;
@@ -110,10 +129,6 @@ bool wxStaticBoxBase::Enable(bool enable)
 
         m_isEnabled = enable;
 
-        // Notice that we don't call DoEnable() on the box itself: under MSW it
-        // doesn't actually change anything and under GTK this would disable
-        // the label window.
-
         return true;
     }
 #endif // wxHAS_WINDOW_LABEL_IN_STATIC_BOX