Use wxString's empty() when checking if the string is (non-)empty throughout wx.

Instead of constructs such as if "( s.length() )" and "if (s.length() > 0)" use "if ( !s.empty() )" instead. Similarly for "if (s.length() == 0)" or "if ( s.IsNull() )", use "if ( s.empty() )".
No code changes intended except for a few instances where a construct like "if ( s.length() && wxFileExists(s) )" was changed to not check the length of the string and let wxFileExists handle such cases.



git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66728 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/propgrid/propgrid.cpp

@@ -322,7 +322,7 @@ public:
         wxString s = ::wxGetSingleChoice(wxT("Message"),
                                          wxT("Caption"),
                                          m_choices.GetLabels());
-        if ( s.length() )
+        if ( !s.empty() )
         {
             SetValue(s);
             return true;