stop PLC before unloading


This fixes segmentation fault if service was quit without stopping it.
It has happened if Beremiz service was quit using taskbar icon or by
closing Beremiz IDE (in case of autostarted local service).

In second case to trigger the bug following step has to be done:
1. Open Beremiz IDE
2. Open project, compile and connect to LOCAL:// runtime
3. Transfer and start the PLC program
4. Open other project without disconneting the PLC runtime
5. Close Beremiz IDE

--- a/Beremiz_service.py	Wed Dec 07 18:32:34 2016 +0300
+++ b/Beremiz_service.py	Wed Dec 07 19:24:16 2016 +0300
@@ -411,6 +411,7 @@
     def Quit(self):
         self.continueloop = False
         if self.plcobj is not None:
+            self.plcobj.StopPLC()
             self.plcobj.UnLoadPLC()
         self.Stop()