Allow returning NULL windows from GetCompositeWindowParts().

wxCompositeWindow::GetCompositeWindowParts() becomes simpler to implement in
the derived classes with optionally shown elements if NULL windows are allowed
(and ignored) in the list returned by it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68910 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/compositewin.h

@@ -110,6 +110,10 @@ private:
         {
             wxWindow * const child = *i;
 
+            // Allow NULL elements in the list, this makes the code of derived
+            // composite controls which may have optionally shown children
+            // simpler and it doesn't cost us much here.
+            if ( child )
                 (child->*func)(arg);
         }
     }

src/generic/datectlg.cpp

@@ -385,9 +385,7 @@ wxSize wxDatePickerCtrlGeneric::DoGetBestSize() const
 wxWindowList wxDatePickerCtrlGeneric::GetCompositeWindowParts() const
 {
     wxWindowList parts;
-    if (m_combo)
     parts.push_back(m_combo);
-    if (m_popup)
     parts.push_back(m_popup);
     return parts;
 }