added wxSafeConvertMB2WX/WX2MB() and use them when interfacing with C functions which crash if we pass them NULL pointers

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@44771 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/palmos/utils.cpp

@@ -90,7 +90,7 @@ bool wxGetUserName(wxChar *buf, int maxSize)
         return false;
     }
 
-    wxStrncpy (buf, wxConvertMB2WX(id), maxSize - 1);
+    wxStrncpy (buf, wxSafeConvertMB2WX(id), maxSize - 1);
 
     // free the buffer
     MemPtrUnlock(id);