wifi trigger, memorize most recent ssid

app/src/main/java/com/jens/automation2/location/WifiBroadcastReceiver.java

@@ -41,6 +41,7 @@ public class WifiBroadcastReceiver extends BroadcastReceiver
 		if(newWifiSsid.startsWith("\"") && newWifiSsid.endsWith("\""))
 			newWifiSsid = newWifiSsid.substring(1, newWifiSsid.length()-1);
 
+		if(newWifiSsid.length() > 0)
 			WifiBroadcastReceiver.lastWifiSsid = newWifiSsid;
 	}