Don't mark WM_CHAR for VK_RETURN as processed if it wasn't

This doesn't seem to change anything in practice, but it's more logical
to not pretend that we processed the message if we didn't do anything at
all with it.

src/msw/textctrl.cpp

@@ -2193,9 +2193,8 @@ wxTextCtrl::MSWHandleMessage(WXLRESULT *rc,
             HasFlag(wxTE_PROCESS_ENTER) &&
             wParam == VK_RETURN )
     {
-        ClickDefaultButtonIfPossible();
-
-        processed = true;
+        if ( ClickDefaultButtonIfPossible() )
+            processed = true;
     }
 
     switch ( nMsg )