OWSWITCH: fix 'Use of uninitialized value in left bitshift (<<) at ./FHEM/21_OWSWITCH.pm line 717.' when being used with OWX_ASYNC

git-svn-id: https://svn.code.sf.net/p/fhem/code/trunk@5523 2b470e98-0d58-463d-a4d8-8e2adae1ed80