fixed crash after device was disconnected

git-svn-id: svn://svn.code.sf.net/p/fhem/code/trunk@347 2b470e98-0d58-463d-a4d8-8e2adae1ed80

fhem/FHEM/00_FHZ.pm

@@ -616,6 +616,7 @@ FHZ_Read($)
 
     my $dev = $hash->{DeviceName};
     Log 1, "USB device $dev disconnected, waiting to reappear";
+    delete($hash->{FD});
     $hash->{PortObj}->close();
     DoTrigger($name, "DISCONNECTED");