Fix wrong code generation if EN/ENO are used in FBD/LD/SFC

This problem appears for example here

--------
------- | MOVE |
| MOVE1 |------|EN ENO|
------- | |
| |
------- | | -----------
| 23 |------|IN OUT|---| LocalVar0 |
------- -------- -----------


--------
------- | MOVE |
| MOVE2 |------|EN ENO|
------- | |
| |
------- | | -----------
| 15 |------|IN OUT|---| LocalVar0 |
------- -------- -----------

Before wrong code was generated for this case:

MOVE6_OUT := MOVE(EN := move1, IN := 23, ENO => MOVE6_ENO);
LocalVar0 := MOVE6_OUT;
MOVE4_OUT := MOVE(EN := move2, IN := 15, ENO => MOVE4_ENO);
LocalVar0 := MOVE4_OUT;

With this patch now following code is generated:

MOVE6_OUT := MOVE(EN := move1, IN := 23, ENO => MOVE6_ENO);
IF MOVE6_ENO THEN
LocalVar0 := MOVE6_OUT;
END_IF;
MOVE4_OUT := MOVE(EN := move2, IN := 15, ENO => MOVE4_ENO);
IF MOVE4_ENO THEN
LocalVar0 := MOVE4_OUT;
END_IF;


See discussion here:
https://sourceforge.net/p/beremiz/mailman/message/36378805/

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# This file is part of Beremiz.
# See COPYING file for copyrights details.

from __future__ import absolute_import
from plcopen.XSLTModelQuery import XSLTModelQuery


class InstancesPathCollector(XSLTModelQuery):
    """ object for collecting instances path list"""
    def __init__(self, controller):
        self.Instances = []
        XSLTModelQuery.__init__(self,
                                controller,
                                "instances_path.xslt",
                                [("AddInstance", self.AddInstance)])

    def AddInstance(self, context, *args):
        self.Instances.append(args[0][0])

    def Collect(self, root, name, debug):
        self._process_xslt(root, debug, instance_type=name)
        res = self.Instances
        self.Instances = []
        return res