Reset the pointer to NULL after deleting it in wxCmdLineArgsArray.

This ensures that a dangling pointer can't be dereferenced later and fixes a
fatal bug if wxCmdLineArgsArray::operator=() was called more than once (which
is however not supposed to normally happen).

include/wx/cmdargs.h

@@ -113,7 +113,7 @@ public:
 
 private:
     template <typename T>
-    void Free(T **args)
+    void Free(T**& args)
     {
         if ( !args )
             return;
@@ -123,6 +123,7 @@ private:
             free(args[n]);
 
         delete [] args;
+        args = NULL;
     }
 
     void FreeArgs()