#145 Default editor related crash in wxPropertyGrid 1.14.13

[Guillaume]

During initialization default editor classes are created but when the application is terminated the default editors are deleted in the wxPGGlobalVarsClass destructor. This frees the memory but does not reset the pointers wxPGEditor_Editorname pointers to NULL. So if one were to use wxPropertyGrid in an external main loop these pointers would never be reset and they would still point to invalid memory. Calling wxEntry a second time causes an inevitable crash.

Resetting the pointers to before first initialization or after deletion would fix the problem.