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

Commit c9915bc6 "Fix wrong code generation if EN/ENO are used in
FBD/LD/SFC" caused following backtrace in some cases:

File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 476, in GenerateProgram
self.GeneratePouProgram(pou_name)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 258, in GeneratePouProgram
program = pou_program.GenerateProgram(pou)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 1713, in GenerateProgram
self.ComputeProgram(pou)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 997, in ComputeProgram
eno_var = self.GetUsedEno(body, connections)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 929, in GetUsedEno
for invar in blk.inputVariables.getvariable():
File "/home/developer/WorkData/PLC/beremiz/beremiz/xmlclass/xmlclass.py", line 1363, in getattrMethod
return DefaultElementClass.__getattribute__(self, name)
<type 'exceptions.AttributeError'>: 'inOutVariable' object has no attribute 'inputVariables'

     1

#!/usr/bin/env python

     2

# -*- coding: utf-8 -*-

     3

     4

# This file is part of Beremiz, a Integrated Development Environment for

     5

# programming IEC 61131-3 automates supporting plcopen standard and CanFestival.

     6

#

     7

# Copyright (c) 2016 Mario de Sousa (msousa@fe.up.pt)

     8

#

     9

# This program is free software: you can redistribute it and/or modify

    10

# it under the terms of the GNU General Public License as published by

    11

# the Free Software Foundation, either version 2 of the License, or

    12

# (at your option) any later version.

    13

#

    14

# This program is distributed in the hope that it will be useful,

    15

# but WITHOUT ANY WARRANTY; without even the implied warranty of

    16

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

    17

# GNU General Public License for more details.

    18

#

    19

# You should have received a copy of the GNU General Public License

    20

# along with this program.  If not, see <http://www.gnu.org/licenses/>.

    21

#

    22

# This code is made available on the understanding that it will not be

    23

# used in safety-critical situations without a full and competent review.